We'd be going with Windows 7, case and PSU don't really matter, as long as their adequate.
Our source code/development environment and deployed application clock in at under 2.5 gig.
SSD's are a good suggestion.
What's the best small SSD? The Intel chips seem to be the best, but their sizes are too big for us to justify the cost. Do SSD's still have issues if you fill them up too much they slow down significantly?
Intel X25-M or X25-E are the best SSDs right now.
SSDs don't slow down if you fill them up. They degrade with writes, reads, and deletes. Basically if you have it as just a boot drive and not saving all your work to it, it would last a little longer.
We have 7 art machines here at work with the X25-M 80gig G2. After 2 months, they are still working fine. I've got one at home too since the release of the G2 and it's still working fine. I play all my games off my Raptor drives though and I run the Intel optimization utility daily.
The Intel SSDs are the hottest thing on the market right now just below the new ATI HD 5800 series cards. They are releasing a new line of SSDs, X25-X which are suppose to be cheaper, but slower (only 170 mb/s, which is still pretty darn fast)