Is it bad to mix RAM?

[SwiZz]

My motherboard is: Asus P4P800-E Deluxe
Link to specifications: http://www.digital-daily.com/motherboard/asus-p4p800-e/

I currently have 2x256MB sticks of Geil RAM. My motherboard has 4 slots apparently for RAM. I was thinking of upgrading to 1GB.

I was planning to buy 2x512 MB of RAM. Probably either OCZ/Kingston/Corsair. Whatever's cheaper I guess.

Would I be able to use my 2x256MB sticks of RAM on top of the 1 GB?

RAM is normally 256, 512, 1GB, 2GB....i never really heart of 1.5 GB of RAM. Is this because its somehow bad to do use that specific amount? And if I decide to do this, will mixing brands cause problems? Should I try to get my 1GB in 2x512MB sticks of Geil?

Don't flame me..i know nothing..lol

Thanks

EDIT: Also is Geil a decent brand these days?

[wonton1017]

Its not good to mix ram, dual channel wont function properly and it might even make your computer slower than having just 2x512mb.
Also, Geil is a pretty good brand, but not as high-end as Corsair, OCZ and Mushkin.

[Amourek]

Should work fine. I've mixed two different brand sets of RAM in the P4P800... never tried two pairs with different sizes though. Still I don't expect any problems.

[162]

I've mixed them - never had any problem - they ran as good if not better!