Go to run and type "services.msc". A list of background services will be displayed and clicking on each will display a brief description. Here is a list of services you can disable if you have a standalone computer:
1.Computer Browser.
2.Messenger.
3.Net Logon.
4.Net meeting remote desktop share.
5.Performance logs and alerts.
6.Network provisioning service.
7.Qos RSVP.
8.Remote desktop help.
9.Remote Registry.
10.TCP/IP netbios helper service.
11.Terminal Services.
12.Wireless Zero Configuration.
13.Smart Card.

Note:Some sevices may be already disabled.
This will free some space on your memory.