I did some exploring on my ibook and found out it actually only has 256mb of ram and not 640mb

Considering its running stuff like OS X Tiger 10.4.11 and iTunes 9.2, latest Firefox etc... its pretty fast

Would upgrading it to 640mb (change the 128mb dimm to 512mb) make a difference as in youtube video playback, loading etc.. ?
Also, the HD is a 30GB... I have a spare pc laptop 120Gb HD which i never ended up using in my A1200. Would the iBook G3 (Dual USB) accept it ?