I clean reinstalled leopard on my macbook pro using the provided leopard disc and selecting the erase and install option. I have an external hard drive with time machine back ups that I want to continue to build on top of. Is that possible? If so how? I've googled around and have found no answer.

The reason I clean reinstalled leopard is that I had less than 4 GBs of free disk space left on my Macintosh HD partition because I failed to accurately predict the amount of disk space needed for programs and updates. Another reason was that finder took a long time to unmount anything plugged in, ranging from flash drives to external hard drives. I had Windows XP on a NTFS partition and a large FAT 32 (which can be read and written to by XP and Leopard) partition taking up most of the disk space. I found I ended up using Windows XP extremely infrequently due to instability of boot camp drivers resulting in random hard freezes, excessive heat when in XP and poor run time on battery. Now I have repartitioned and the result is a much larger partition as Macintosh HD and a Data partition formatted HFS+ journaled which is supported by time machine as opposed to FAT 32.
I also had time machine back up an external hard drive I use to store photos on. The data on that drive has not changed much since my clean reinstall, I imagine time machine should be able to scan it and find where the differences lie and update the back up in only those parts.
After my clean reinstall I have reloaded almost all of the programs and data back onto my computer. In my mind there should not be much difference between the previous Macintosh HD partition and the one now, I imagine time machine should be able to scan it and find where the differences lie and update the back up in only those parts.
Besides updating backups, I imagine time machine will run a full backup of my newly created HFS+ Journaled Data partition.

I could erase my entire time machine drive and start over but I really want to be able to look back in time at the state of my pre-repartioned system in case there is something I still need. An example is my Stickies which I forgot to manually back up, thanks to time machine, I was able to go and recover them.
Also, I don't have enough free disk space on my time machine drive to have two full backups of all the partitions.

Help on this issue would be greatly appreciated. Thank you.