After reading other posts, it looks as though using DDR2 sticks with different speeds is okay. Is this right? If so, should I try to be consistent anyway? Is there a benefit to carefully selecting the same speed DDR2 when adding ram to my PC?

Hi Kento...

You are correct. Different speeds of memory have no effect on the stability of ones system.

There is a benefit..it means both memory runs at the same speed...
Basically if you buy brand new low CAS speed memory, it will run at the slower speed, but if you buy new slower memory, the older faster stuff will slow down to the same speed.

Thanks! I appreciate your help and have a follow-up question... Is it better to install one 1gig stick or 2 512 Mb sticks? (Or does it make a difference?)

No problems

2x 512mb is better for 1gb, so you get "Dual Channel" which means it access the ram faster.

That makes sense. Thanks!
btw, I've enjoyed reading your other posts. A sense of humor is a huge asset when dealing with frustrating PC problems...
I guess I'll go buy some RAM now.

Hahaha, thanks for the great comment

You should hear me on phone when talking to angry customers....who - i might add - can see exactly what i'm doing on their computers while speaking to them...it's actually rather daunting, but unless they start the conversation with a swear word, they end up smiling