Your G4 is NOT a Quicksilver model. There has never been a 550 Mhz model, so I have to assume it's either the original G4 AGP, gigabit ethernet or digital audio model. In any case, a company called Other World Computing has a series of CPU (processor) upgrades that can be purchased and installed into your Mac. Pricing starts around $200 for 1.6 Ghz CPU upgrade, $350 for an 1.8 Ghz CPU and $399 for a 2.0Ghz CPU, respectively.
http://eshop.macsales.com/search/MaxPower+G4
The 1.6 Ghz upgrade is a great price, IMHO, and would more than double the speed of the processor already in your Mac.
The other 2 CPU upgrades almost approach the cost of a new Mac mini.
Since this Mac is very old, you would have to weigh the cost of the more expensive CPU's versus looking for either a new Mac model or purchase a used, but much newer G4/G5 with better specs and more power.
There are newer technologies available in newer/used G4/G5 Macs, that would give you a faster Mac and more without spending money onmore expensive new Macs.
It would be more cost effective to look at purchasing used/newer Macs(if you can't afford a new Mac) than to put money into your aged PowerMac G4.
While $200 for a CPU upgrade isn't all that expensive, everything else in your Mac that can't be upgraded will be a factor in how much faster your Mac will actually be after the CPU processor upgrade.
May not be as fast as you may think.
The system bus (thru data pipeline) speeds at the lowest/worst is 100 Mhz. The highest/best system bus is only 133 Mhz. Later G4's top out at 166 Mhz. Later Macs such as the G5 line top out at 1.25 Ghz!
You'll need to decide whether you really want to spend money on a aging Mac or use your cash+ to invest in a new/newer more capable Mac.
