First of all, The hard drive in your performa uses an interface known as SCSI . The iMac you will be getting uses IDE, because of this, you will not be able to swap the drives. Also the iMac most likely has a 6 gig drive. Not to mention the performa uses apples achient monitor interface, which was dropped with the introduction of the Blue and White G3 I beleive. If you already have file sharing enabled on your performa, you can just connect both to a hub and connect to it that way, long as you don't mind running your mac headless. You might as well leave the ram and optical drive in the performa, because the optical drive also uses the same SCSI interface as the HD. The RAM is either 72 pin ram, which makes a good keychain by todays standards, or PC66 168 pin RAM Which is pretty much useless, unless you have an old PC. But, If file sharing fits the bill your not totally screwed.
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Mobile-2.2Ghtz Core 2 Macbook, 4GB ram, 160GB HDD
Server-Dual 1.42 MDD G4, 1GB ram, 4 random hard drives.
PC-C2D 2.4Ghtz, Asus Commando, 2Gb ram, 3 hdd's in raid 5, 8800GTS.