Help! with Western Digital HDD

It's going on six hours I've been trying to sort this out.
Here's what's happening (and I'm sleep deprived at this point and may likely leave out some critical information).
I have a Macbook pro. I have a 1TB WD MyBook (or something) HDD usually accessed thru the USB port on my Airport Extreme. This is nice. I came home from dinner tonight with the intention of watching some television I'd downloaded, only to find that my computer was wholly incapable of opening a 350MB file from the drive. Quicktime froze, had to relaunch finder, etc. I restarted the computer and tried again. No dice. Dismounted the drive, remounted. Same. Tried different ports, firewire, different cables, etc. Repaired my internal HDD with OnyX after booting in single-user mode. Scanned both disks for errors and Disk Utility says both are working just fine. No scary clicks of death or any funky noise or anything.
I can view the file structure on the drive after it's been mounted and indexed. The files are there, but to do anything with them takes ages. I was able to open a small mp3 after about two or three minutes, and managed to copy a word document to my desktop after a little while, but my computer can't seem to handle it. I've got a 2.5 Ghz processor and 4GB of RAM. The external drive IS 97% full, but was 97% full yesterday (and the week before and the month before) and was running fine. I haven't run a defrag on it, but I don't constantly save files to it. It's mostly storage only, and I can't imagine it's THAT horrifically fragmented. Even if it were, it wouldn't suddenly run so sluggishly. It's almost 3 am where I live now (Taiwan) but I want to take it to the Apple store tomorrow and see if it's the same with other Macs. My internal drive (250GB) has 11GB free on it, but again, nothing drastically changed to cause everything to become inoperable so suddenly. I was worried the drives were (freakishly) both somehow going bad, but again, all the file structure and everything is there. I just can't seem to access it without gumming up the works. WHY? I want to try a firmware update on the external, but not until I've got everything backed up.
Other useful information... I'm running OS X 10.5.8, I have a small Windows XP partition on my internal disk. I was worried about bad sectors or something, but after scans and repairing permissions and more scans, disk utility (and Onyx) says all is well.
Would both discs being nearly full SUDDENLY cause them to be so non-functioning? Please help!
Apologies for leaving out any other critical information.

If your internal boot drive is nearly full things start getting wonky.
If the system doesn't have space to write cache/tmp/virtual memory files things slow way down.
Even to the point of not working at all. Try and free up some space on your internal.
Some people recommend at least 15% free space.

Take the wifi out of the equation for the sake of trouble shooting. If the results are back to normal with the ext HD going straight into the MBP, then you need to trouble shoot the Airport device. I would however recommend (either way) trying to free as much space as possible on your internal drive, as that is the drive likely being used as a "scratch" disc. Meaning where all temp files (or not temp) are stored for the cache.


Doug

Thanks, guys. I took AEBS out of the equation and connected it directly; tried both USB 2.0 and Firewire.
Before I tried messing with it again (not necessarily BECAUSE of this issue, just because) I upgraded to Snow Leopard and cleaned about 15GB off of my internal disk. I bought a new external 2 TB Western Digital drive and formatted it and everything. It has a Time Machine partition backing up my internal drive.
The 1TB drive did freeze Finder in Snow Leopard once (and seems to have just done it again trying to eject the problem drive). I'm getting the "can't be read or written" error code -36 message on a lot of my test file transfers (trying to transfer 300mb quicktime files before my 150 GB folders), and it's taking those even like 15 minutes to transfer, assuming they finish. Thumbnails for files take forever to load, and sometimes finder won't show the contents of a file for ten minutes or so. Deleting files (regardless of size, seemingly) takes forever, as well, but I've got about 56gb of the 1TB (or technically just shy of that) free now... it happened so suddenly. it was never like this before. Could my drive be taking its last breaths? (It's making no horrific "I have hardware issues" or "my arm is broken" noises or anything, and was fine one day before I went to dinner, and I came back and it wasn't... how could this be?!

Go go gadget DiskWarrior

Just rebuilt the drive with DiskWarrior and there's still no change to it. Could the fact that it's 94% full really cause it suddenly be so sluggish as to be inoperable? DW said there were no issues with the drive. Fixed some file permissions or something, but it says the drive is ok, just as Disk Utility did. Takes forever to prepare to copy or view contents of a folder, and more often than not the copy is aborted because of the "can't read/write" error I mentioned above. Was hoping DiskWarrior would do it, but all sources say the drive is just fine, which I suppose is GOOD news, but... it doesn't seem fine.

Hate to keep posting replies to myself, but I'm working on trying to get this done. Copying the problem disk to a new drive with SuperDuper, but noticed that spotlight is CONSTANTLY trying to index the problem drive. More accurately, it's always "estimating index time." I don't know if this could be the problem (keeping the drive busy) or just another symptom of whatever the problem really is.
I came across SuperDuper and people have extolled its virtues. After 90 minutes, it's got only 4GB of 800GB done, with an effective copy speed of .78MB/s and seeming to drop. I might be here a while.

[Edit: Added problem drive to the privacy list in Spotlight preferences, and although this is apparently only temporary, it doesn't appear to be indexing anymore. However, this has done very little to change the rate of transfer]