You can also try some things:
  1. Clean all the crap using CCleaner (CrapCleaner). It can be found here(usually Tosko is the first to notice!), or at it's home page, or at Fillehippo.com. It should be found in the "freeware section". Try it first to get the hang of it , and use it at startup later. It is small and fast. You will be amazed, I am sure.
  2. Defrag the HDD!
  3. Download Microsoft ® “Bootvis”, and use it to monitor/change the startup-sequence.
  4. Download "Microsoft ® Baseline Security Analyzer", as it will tell you if your system is up-to-date.
  5. You can also monitor/change/stop the services that are running. As some are needed, and some are not, I have made a list of the most used ones!
This is how it works.

Instruction :
Go to <Start>, <Run>, type "services.msc" and press <enter>.
Left-click on the status bar twice to filter all the started service to the top.
Double left-click on the Service Name you wish to change.
Change the "Startup Type" to either Automatic, Manual or Disabled then select <Apply> and <OK>, repeat for all of the following:

Disabled - The following is a list of Services that you can disable on most systems:
  • Alerter
  • Distributed Link Tracking Client
  • Help and Support: If you use Windows Help and Support leave this enabled)
  • Indexing Service
  • IPSEC Services
  • Messenger: Shoot the Messenger and installing SP2 will disable this.
  • Portable Media Serial Number: Leave enabled for use with security dongles.
  • Remote Registry Service
  • Secondary Logon
  • SSDP Discovery Service
  • Upload Manager
  • Wireless Zero Configuration: If you are on a wireless network leave this enabled.
Automatic - The following is a list of Services that should always be set to automatic:
  • Application Layer Gateway Service: Required by the Windows XP Firewall.
  • Automatic Updates: Required by Windows Updates.
  • Background Intelligent Transfer Service: Required by Windows Updates.
  • COM+ Event System: Required by BootVis and other applications.
  • Cryptographic Services: Required to confirm the signature of Windows system files, protected root services and key services.
  • DCOM Server Process Launcher: Required by the Disk Defragmenter.
  • DHCP Client: Required for Cable/DSL connections and routers.
  • DNS Client: Improves internet performance.
  • Event Log: Required by Windows and cannot be stopped.
  • Logical Disk Manager: Required to manage and update your harddrives.
  • Network Connections: Required by network connections.
  • Plug and Play: Required by your system hardware, Never Disable This!.
  • Print Spooler: Required by printers.
  • Protected Storage: Required to protected sensitive data and to prevent access by unauthorized services, processes, or users..
  • Remote Procedure Call (RPC): Required by Windows, Never Disable This!.
  • Security Accounts Manager: Required to store security information for local user accounts.
  • Security Center: Notifies you of you Firewall and AntiVirus status.
  • Shell Hardware Detection: Required by the AutoPlay feature.
  • System Event Notification: Required by various applications.
  • System Restore Service: Required by the System Restore feature.
  • Task Scheduler: Required by the Windows Prefetcher, BootVis and Norton AV, Never Disable This!
  • Themes: Required by the new look of Windows XP.
  • Windows Audio: Required for sound.
  • Windows Firewall/Internet Connection Sharing (ICS.: Required by the Windows XP Firewall.
  • Windows Management Instrumentation: Required by Windows, Never Disable This!
Network Services - The following is a list of Services that are required on home networks and LANs:
  • Computer Browser: Locates local computers and resources on a LAN.
  • DHCP Client: Required for Cable/DSL connections and routers.
  • Network Connections: Required by network connections.
  • Server: Required for network shares and managing local user accounts.
  • TCP/IP NetBIOS Helper: Required for NetBIOS name resolution.
  • Wireless Zero Configuration: Required if you are on a wireless network.
  • Workstation: Required for access to LAN shares and servers.
Notes:Windows Updates can enable services that you have previously disabled. Check which services are running after a future Windows Update is completed. If applications stop working after this it is usually due to being to aggressive with disabling services. Enable the services you disabled one at a time until the application works. In the future leave this service on automatic. If you run into any problems set all services back to their Defaults and start over.