I open up the CS and load up oblivion.esm and the .esp i am working on, setting the esp as the active file. Any time I try to save, the CS comes up with the standard windows vista crash message.

I have 2gigs of ram, dual core processor, and the cs takes up barely 5% of the cpu.
The esp i am working on contains extensive modifications to the landmass, new interior cells, new meshes, and new textures.

Any help that can be offered or any direction in which to look for specific crash information would be appreciated.

The CS doesn't handle large plugins very well. You could try moving some of the content to an master file.

Also take a look at the http://cs.elderscrolls.com/constwiki/index.php/Category:Troubleshooting.

The plugin I am working on is very much a work in progress, and the esp itself is only around 1-2MB.
Should i stop where i am, convert what i have into a master file, and then make any future work into an esp that i then merge with the master?

1-2 MB is not a problem, with large I meant several hundred MBs.

Maybe this page has some useful information: http://cs.elderscrolls.com/constwiki/index.php/Windows_Vista.