 here is a list of services that can be turned off
this will speed up your pc a bit

right click my computer
manage
services and applications
services

set these to disabled you will need to reboot for them to take effect if you have a problem with any just reenable them again ie if you have a smart card and you disable it wont work

alerter
application layer gateway service
application management
ati hotkey poller
automatic updates
background intelligent transfer service
clipbook
com+ event system
com+ system application
distributed transaction coordinator
error reporting service
fast user switching compatibility
help and support
human interface device access
imapi cd burning com service
indexing service
internet connection firewall(icf)/internet connecton sharing(ics)
ipsec services
logical disk manager
logical disk manager administrative service
messenger
ms software shadow copy provider
net logon
netmeeting remote desktop sharing
network dde
network dde dsdm
nt lm securtiy support provider
performance logs and alerts
portable media serial number service
qos rsvp
remote desktop help sesson manager
remote registry
removable storage
secondary logon
security accounts manager
server
smart card
smart card helper
ssdp discovery service
system restore service
task scheduler
tcp/ip netbios helper
telnet
terminal services
uninterruptible power supply
universal plug and play device host
upload manager
video proes
volume shadow copy
webclient
windows time
wireless zone configuration
wmi performance adapter
workstation