iMAC PAV board

How difficult is replacing the PAV board in an iMAC G3?
Should I tackle it myself?

This is a major repair. This is far beyond replacing the hard drive or CD. You would have to dissassemble the case and remove several internal components, including the CRT. Outside of dealing with the high voltage, you can de-calibrate the CRT if its internals are dislodged. You might want to find a take-apart manual (try Google) to get a better picture of the procedure. IMO, given the difficulties involved and the age of the iMac I'd let this one go.