Firstly, you would be well advised to get OS X and more RAM.
All the crashing is the result of not having enough RAM, but in
OS 8 -9.x, RAM is not allocated dynamically as it is in Windoz.
If you want to stop the browser from crashing, you have to
allocate more RAM to the browser. It sounds very primitive,
but all of this is fixed in OS X (but you still need lots of RAM -
it's not an Amiga:)
Secondly, a G3 is probably only a little faster than a P3 at the
same MHz, so the iMac is not a speed demon by any measure.
Check out places like macsales.com for better prices on Mac
OS upgrade CDs (9.1 or 10.1 $40, etc).