I recently installed a LTSP server on one of my hard drives on my desktop. I hooked up a laptop using a standard cat5e cable to my second network card, booted the desktop, then booted the laptop from network.....voila! it PXE booted the laptop right into my thin client. Now my question is how do i administer / control the thin client using my desktop (server)

The ltsp server is Ubuntu 10.04 (ltsp edition) running with 6gb ddr3 ram, intel i7 quad core processor. this is really irritating, any help would be greatly appreciated

you probably can't unless the thin client's file system is a network share, in which you would simply edit the config files for the thin client directly on the server, but the operative word here is CLIENT, thus it more than likely doesn't have any daemons listening on the network to log into.
The question is what kind of administration would you be doing on a thin client since by definition it's a glorified display and all the programs are being run on the server?

I mainly use it to try and repair other people's laptops, I would like to boot them from my desktop, and be able to control them from there, whether its running a virus scan or backing up data, accessing the hard drive, etc....

well in that case, 'thin client' isn't really the word for it, in which case you would install vnc server into your network boot setup and connect to it from the main machine
this of course assumes the laptops are capable of booting from their network cards.