I've done searches but i don't really see any limitations. on software raid and linux...

but i have a 166mmx pc with 128 meg ram and two 2.5gig hard drives and i've set it to use mirroring on both drives. But when i add the second drive it seems to lock up or just lag. both drives are functioning properly. It seems to be responding but very slowly

I solved the issue by moving the drives into another pc with simmilar pecs but a faster processor, 1.2ghz and now everything seems to be fine.

But i'm still wondering if there was anything else that i could do? Because i like the other pc because it isn't as loud.

Was this a limitation on my pc because of the older/slower hardware?

Your processor was likely the pitfall of the raid setup. It is likely that you would want about 500MHz to do software raid, and that 500MHz would probably be at 80% usage for a lot of the time.