VERY slow & intermittent internet connection

I have a 2008 iMac. Up until the past month or so, I have had not problems with my internet connection (I use Firefox). We recently upgraded to Snow Leopard, then Lion. I upgraded my memory from 1GB to 4GB to do the Lion upgrade. I also bought a backup hard drive and started using Time Machine.

My internet connection is driving me crazy. I used to have 'airport' icon, now it says wi-fi and it is often disconnected, or sometimes self assigns an IP address that isn't correct. Loading a regular page can sometimes take forever, let alone trying to watch a video.

I turned off the Time Machine, to see if that might be the problem, but it is still slow. Is there some setting I need to correct once I switched to Lion? I've tried to look at the Network preferences, but it all seems kosher (although I am definitely not an expert).

Argh! Can anyone give me an idea on where to adjust something, anything??

I'm sorry I don't have a clue. I am having a problem along these lines though. Due to a recent power outage, my Linksys router had to be reset by a technician. Since this happened (yesterday) my connectivity SUCKS. I cannot watch videos or movies because the buffering will not stop and I can not just load the stream. Just the other day I was enjoying Hulu movies while I did my sewing. Forget that now. I was hoping someone could tell me if I need a new router or if the technician was remiss in some way...or what.
Thank you, oh mighty clever ones.

Talk about a late reply, but since I stumbled upon this post while trying to fix a similar problem, thought I'd post what worked for me. storeagent was downloading something big in the background.

Generally, for unusually slow internet connectivity, use nettop(1) in OS X to figure out which process is choking the internet bandwidth. It is pre-installed.

In the Terminal:
$ nettop
Then hit 'd' and look for entries with consistently large values in the 'bytes in' or 'bytes out' column. The 'd' instructs nettop to only show differences in each screen refresh.

Practical usage notes:
If you don't recognize the process name, Google it.

If you don't want the process around, get the pid (the number next to the process name in nettop), and kill it with "kill -9 <pid>". If that doesn't solve it, find out if you can politely tell the process to stop (for e.g. I logged out of AppStore, iBooks, iTunes and killed storeagent again).