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Hi guys!
I don't know why but BG and BG 2 work soooo slow when I cast spells!!

Are you trying to run BG on a newer operating system or with a newer graphics card? I was having the exact same problem (slow frame rate) when I installed BG2 on my new laptop a few days ago. I solved my problem by turning off hardware acceleration. It's possible that my solution could also solve your problem.

The second post in that thread explains the step by step process for turning off hardware acceleration. It's kind of annoying, but I think it has solved the slowdowns. Try it out and let me know if it works for you.

NOTE: This was a fix for BG2, I have no idea if it would also fix your problems with BG1, although it's worth a shot.