Well I just installed Vista and I really like it, unfortunately I don't have much RAM (768MB) so it runs a kinda slow. Now the first time I upgraded my RAM I really didn't have a problem, just went online and found it right away. This was a couple years ago. I'm looking online now and I can't find a single thing for my computer.

It's RDRAM and I have four slots. Two slots have 128MB and two have 256MB. Here are the complete specs-
Module Manufacturer: Samsung
Module Model: MR16R 1628EG0-CT9
Module Type: RDRAM / RIMM Module
Module Speed: 533 MHz (PC-1066)

Can someone find me something that will be compatible with my computer online? How much RAM do you recommend I get? I'm thinking just 1GB total, because my type of RAM is extremely expensive. What do you guys think?

Have a look here Rory;
Memory upgrades, graphics cards, flash media, and usb storage at Crucial.com

I ran the scanner and it says "According to our scan, your system already has the maximum amount of memory installed.", however my system can handle 2GB maximum.

What is the make and model of your motherboard and i will check this for you.

Computer Brand Name: Dell System 8250 (Dell Dimenson 8250)
Motherboard Model: Dell Computer Corp.
Motherboard Chipset: Intel 850E (Tehama-E) + ICH2

oh you dont actually know the motherboard name - that is just dell's name for it. If possible could you open the case and look for the motherboard make and model on the actual motherboard, it will be printed on there somewhere.