Vista - what background services can I stop?

I am trying to find out the cause of intermittent sluggishness on my
laptop (1.5 celeron M, 1Gb ram, 128mb integrated graphics)

I have the following services running on my machine...

SamSs
Protected storage
Plug and play
Dcomlaunch
wudfsvc
webclient
w32time
upnphost
ThreadOrder
nsi
netprofm
LanManworkstation
FDresPub
fsphost
EventSystem
wscsvc
lmhosts
eventlog
dhcp
audiosrv
MpsSvc
DPS
BFE
WPDBusEnum
Wlansvc
WdisSystemHost
Uxsms
TrkWks (what is this? says its distributed link tracking client, am I
being tracked?)
TabletInputService
PcaSvc
Netman
EMDMgmt (readyboost?)
Cscservice
AudioEndPointBuilder
Wsearch
WMPnetworksvc
SysMain
stisvc
Spooler
slsvc
3 avast entries which I know I need
wuauserv
Winmgmt
Themes
ShellHWDetection
SENS
seclogon
Schedule
Rasman
Profsvc
MMCSS
Lanmanserver
iphlpsvc
IKEEXT
gpsvc
Eaphost
BITS
Appinfo
AeLookupsvc
Termservice
TapiSrv
Nlasvc
KtmRm
DNS Cache
Cryptsvc
Policyagent
RPCSs (why is this running when RPC caused problems with XP?)
WinDefend
Wersvc

Now I am pretty sure that alot of these are not needed but I am
concerned about disabling them in case I screw something up. Can anyone
please tell me if any of those can be stopped from running automatically?