You will definitely need a new computer when upgrading to CS5.
My guess is that your current computer will be around 60 - 80 times slower than a fast PC or even more. Look here: PPBM5 Benchmark It will end up near the very bottom of this list of 210+ systems.
Welcome to the forum.
Along with that old CPU, the 2GBRAM is probably not even enough to run Win7-64, let alone run any programs, like PrPro.
I am with Harm.
My CS5/AVCHD 1st Impressions http://forums.adobe.com/thread/652694?tstart=0 includes a link to the computer I built... since the GTX 285 is no longer sold, I would now go with a GTX 460 or whatever is the current "best bang for the buck" - AND I would buy 4Gig-by-3Sticks memory to be able to expand from 12Gig to 24Gig if needed
For my home hobbyist, family movies (which means that I am not trying to recreate Star Wars with video effects or many layers) AVCHD editing is "as smooth as spreading warm butter on hot toast" (also the MP4 video from wife's Flip camera)
My 3 hard drives are configured as...
1 - 320G WD Win7 and all programs
2 - 320G WD Win7 swap file and PPro projects
3 - 1T WD all video files... read and write