I Have a g3 600mhz imac with a 4 gb hd. I need to upgrade from 10.2 to 10.3. Can i erase the current os while instaling the new os, or do i need a bigger hd to update the os?
Hard rives are so cheap you can get a bigger drive for nearly free. People are pretty much giving away 10GB drives and you can pickup a 20GB for very cheap. There isn't much reason to be stuck on the 4GB drive, unless you have absolutely no other resources. You'd be able to keep your old drive as-is as a backup and put int he new drive and install 10.3 to it. The biggest issue with upgrading to a higher OS X version is your RAM. 10.3 would need 256-512MB to run well.
thanks, i have 512 in the computer right now, is there any specific kind of drive i would need to buy? (brands, sata, that kind of stuff)
You'll need a regular 3.5" PATA, as SATA won't work. You'll also need to use a drive smaller than 128GB, unless you want to use special drivers to see all of the drive. Seagate is a good brand, and if you buy new it'll have 5 years of warranty. Used, of course, will have what is remaining from when it was sold.
I've had very good luck with Western Digital also. If you buy used, make sure you get the original receipt, or the warranty will be void.