Well... can you show me the guide you used? I'd be interested to see it so I can see how bad it really it too.. You have to be careful with this stuff too, you can't turn off stuff that looks really important, even if a guide may say it's OK to but gives some kind of warning.. It's not a good idea to turn a bunch off at once either as that makes it hard to undo what you did.. But still you should have still been able to boot into safe mode, unless this guide had you fucking with things in the registry for some dumb reason (even then I would think you should be able to get into safe mode...) In any case you clearly did something wrong/ you weren't supposed to.
http://www.theeldergeek.com/services_guide.htm
http://www.blackviper.com/WinXP/servicecfg.htm
These two should be very good guides.. Blackviper in particular has been around for a long time and is a pretty trusted source as far as I can tell.. You have to be careful and follow any instructions, take heed of any warnings given, etc..
some standard things I turn off are System Restore (I don't use it), Remote registry, Messenger Service, DHCP server (I use a static IP), Wireless Zero (I use a hardwired NIC and WZ always screwed up the connection every 60 seconds from what I remember), UPnP (security risk).. I very rarely tweak the rest cause I don't feel like experimenting with crap myself..