Developer Rig - Visual Studio 2005 - Suggestions?

Ok, it's time for me to consider a new rig for my developer needs.

I am a straight Microsoft developer with Visual Studio (2003 and 2005) with SQL 2000 and 2005.

I am currently running this on a Windows 2003 Server OS - I am willing to stay on this unless Vista makes more sense.

My real questions:

Stick with Win2K3 (like I have now) or look at Vista? I only do web development work and 32-bit at that. No 64 bit stuff, but I am not opposed to moving to a 64bit processor.

Is a quad core worth it for development work?

Can someone take a crack at suggesting a build out that will be around $1200 (no monitor needed - I already have one)?

No gaming required - I have a gaming rig just for that. Obviously basic sound for watching video tutorials, etc.

No graphic work - such as encoding, etc. Although I may want to learn Silverlight in the near future - not sure what impact this would have.

Will 8 GB really be that much better than 4GB? I only have 1 now, so it'll be dramatic just getting a fast CPU and 4GB!

HD can be around 750GB - I've got plenty of NAS space, so local space is not a big concern.

So much info in this forum revolves around gaming rigs (which is great!) I am a bit at a loss for a quality developer rig (also, I have not built a new system since 2002). I am *really* out the loop with these dual core this and quad core that.  

Thanks all!
Dave