Upgrade's for Powermac G4?

I acquired a PowerMac G4 from a family member. Is this upgradeable? If so, what upgrades should I do and what would it cost? Thanks

23" Apple Cinema Display
OS Leopard 10.5.6

Machine Model - Power Mac G4
CPU Type - PowerPC G4 (2.1)
CPU Speed - 933 MHz
L2 Cache - 256 KB
L3 Cache - 2 MB
Memory - 1.25 GB
Bus Speed - 133 MHz

Mate don't spend too much on it. Memory will only go out to 1.5GB maximum and CPU upgrades are very dear and it will still be a G4 at the end of the day. Maybe look at a faster graphics card, say an ATI Radeon 96500 or 9800 Mac Pro.

How easy is it to switch out graphics cards?

Very. Open her up, undo the single screw that holds the AGP graphics card in place and jiggle it out. To replace seat new card firmly, position screw slot and re-insert the screw. Depending on the card installed, some have a hook like arrangement on the rear od the card, that is the part furthermost from the back of the machine. Lift front of the car first and then move forward to disengage the hook.