You should fill out the PC spec list on OP so we know what you're working with at least. For you to choose DDR2 this enthusiastically is making me go hmm.
Your Current Specs:
E8400 3.0GHz / 4GB (2x2) DDR2 / Asus P5Q Pro / GTX 260 (probably a 560 Ti by next week) / Forgot my PSU, but it's around 600-700 watts / Just an old Antec case
Budget: n/a, just upgrading some things piecemeal with no intent to do the whole thing
Main Use: Rate 1-5. 5 being Highest: Light Gaming
5, Gaming
4, Emulation (PS2/Wii)
2, Video Editing
1, HD Streaming
1, 3D/Model work
3, General Usage (Word, Web, 1080p playback)
5. Also various digital art programs (Photoshop, Painter, etc.)
5
Monitor Resolution: 1920x1080
List SPECIFIC games or applications that you MUST be able to run well: Is 30FPS acceptable? 60? 120? Will you use CUDA accelerated software?
Bad Company 2 and Skyrim are probably the most taxing game for right now, maybe also Battlefield 3 later on. 30FPS is fine, 60 would be nice.
Looking to reuse any parts?: List make and model (e.g. Corsair 520HX 520W, 640GB SATA HDD, Antec 900)
Not rebuilding the whole system, so pretty much everything is remaining in use except the various pieces I want to add.
When will you build?: What time frames are doable? Are you building this weekend? Do you need it in a week or so? Can you wait a month or two?
n/a
Will you be overclocking?: Yes, No, Maybe (This means yes!)
Occasionally, but just the CPU.