Can I run my PC this way?

I have a 512 of 133 and was wondering if I could put that in along side two other 256s,it is the same type as the 256 cards,but haven't added it yet for I wasn't sure what it would do.I don't want to mess up my PC..
Thanks again..

If I understand you right... you want to add another 512 mb of memory? Well as long as your mobo supports 1 gig of memory then yes... Best thing to do is put it in and see... It won't harm the computer any.

Ok thanks,i will give it a shot..