I am trying to upgrade the RAM on my parents' Dell Dimension 8250 desktop (shipped back in late 2002). According to the original specs, the computer came with 2x256 MB of Rambus RDRAM (533MHz, 128X16, 8C). I would like to upgrade the computer to 2x2048 MB sticks for 4GB total. However, I'm confused by all the options (DDR, DDR2, DDR3, etc.) and I'm not sure which types will be compatible with the computer. Any help is appreciated.

2 minutes of googling + reading returned this -

Dell's specs on your machine

It tells you what types of RAM you can use and how much.

Good luck finding RDRAM to put in there. I usually buy from NewEgg, and I can't find ANY RDRAM on their site.

I don't know if DDR2/DDR3 SDRAM is compatible but I wouldn't count on it.

(edit) Initial Google searching indicates that even 1GB sticks of RDRAM are EXTREMELY EXPENSIVE compared to SDRAM (which is what most computers use). So much so that you might be able to buy a brand new computer for cheaper.