Processor speed wont prevent you from doing this as each node acts independently rendering its frames one at a time.

I dont know a great deal about Spider yet, but reading the limited docs it looks as though you can select the machine priority for receiving frames, therefore you should be able to give your most powerful machine the highest priority so that it will receive more of the frames. This should prevent your total render time being dragged out by your slower machines.

Both MayaBatch and Spider require an NT/2000 operating system so WinXP should be fine. Windows 98/95 machines will have to be upgraded to an NT based o/s.

Spider can also split frames up and distribute them around the network for rendering. This means you should be able to render one frame across your entire "farm" - speedy!