RAM is a definate first upgrade option. As of this writing, 256MB is about $49.99.
Processor Upgrade is slightly tricky. There are no upgrades for G4's past 500MHz, because of a problem in motherboard design not letting chips function past that speed standard (it's the 9x multiplier, new G4's have a 14x multiplier). For the B&W;, there is no Dual Processor upgrade, unless you can get a CarrierZIF (try XLR8 for that item) card. The Sonnet G4/Duet card ($699) only works in Sawtooth/Gigabit G4's.
Video cards are very limited. Right now, there are two good choices for graphic cards as an upgrade from the Rage 128. First is a Radeon PCI 32MB DDR ($169), and second is the Radeon 7000 ($129). The difference is the Radeon 7000 is similar in performance to the Rage 128. Unless you really don't care about graphics quality and the fastest framerates, go with the Radeon PCI here.
(Note: Jules, the nVidia GeForce2MX, although a great card, is AGP only, so will only work on Sawtooth G4's or better. Same with the GeForce3's and Radeon 8500)
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