Originally posted by: gwag
has to be you got a blue and white, a bigger faster HD is you best upgrade, it has 4 ram slots its not picky about ram, if your lucky most 300's were made by IBM and are way under rated if its an IBM you'll likely get it to 400mhz no prob. OS X is great I would go for 384M of ram with it sounds like you have it. you may be better poking around @ xlr8yourmac.com than asking for info here, a lot of misinformation has been posted above. be carefull if you get a rev1 motherboard they can have HD corruption issues with some drives.
video card upgrade is not worth the cash unless you get one cheap (used or flash a 7000) and it really only will help out with games not the OS or 2d stuff quartz extreme can be made to work on PCI cards (radeon class) but I dont think its worth it(been there done it)
further info:
http://www.xlr8yourmac.com/G3-ZONE/yosemite/newfeatures.html