Like most people who are interested in getting the best out of W2k I was greatly interested in the services. Many sited recommend disabling them to decrease boot times and to free avaliable ram. However, after doing what this site suggested (changing many supposedly needless automatic services to manual)I was unable to access my isp's server. I could connect, but it was not communicating with my computer at all, I would only receive constant DNS lookup errors. I tried everything, in the end reinstalling the tcp/ip stack in windows 2000 was the only way to fix this. I've seen the same list of services 'safe to disable' on many sites so be cautious.

Messing with services is NOT a bad idea. Messing with the wrong service IS a bad idea.

www.tweak3d.net has a nice services tutorial about services..and what they do

Ok, let me rephrase that, messing with services is NOT a bad idea - If you know exactly what consequences disabling a particular service concurs. I didn't. Still don't.
Many American ISPS automatically assign DNS numbers to their clients upon connection. Mine doesn't however, I have to use a set DNS number. Changing DNS client to manual screwed up my DUN connection because with my ISP, I have to log on to a network. Windows apparently thinks it's a 'windows 2000 domain' anyway.. it's complex, and I don't know much about it.