I am trying to purchase 4 separate RAM sticks that are each 1GB. I have a Microsoft Windows XP Professional/Dell Precision T3400/Intel (R) Core (TM) 2 Duo CPU. I simply need to figure out which particular RAM gigabyte stick that I need to purchase.

I looked up that particular Dell model and found this: "Four DIMM slots support up to 8GB dual-channel DDR2 667 or 800MHz non-ECC and ECC memory" Accordingly, I could go with PC2-6400, a.k.a. DDR2-800.

I second that. Crucial is some of the best RAM in the business. Use their memory finder, enter your system model or information and it will show you the correct sizes and limitations of your PC. Why do you want 4 separate when you get better performance and lower cost from a set of two 2GB DIMMS? 4 DIMMS in the same machine just slows things down by 5% vs 2 DIMMS. For best results choose PC2-6400 http://www.crucial.com/store/listparts.aspx?model=Precision%20Workstation%20T3400

it would depend on the motherboard you have, find the make and model no. of your motherboard and then you will be able to establish what ram is compatible, me personally wouldn`t go for 4 sticks of 1 gig ram i would go for 4gig sticks

http://www.crucial.com has a scan for your computer. It scans then tells you what will work =)