Windows 7, when running with the features as Windows XP, has the same requirements and performance.
You can turn off:
- Application Experience
- Certificate Propagation
- Desktop window Manager Session Manager
- Diagnostic Policy Service
- Function Discovery Host Provider
- IP Helper
- Network List Service
- Netowrk Store Interface Service
- Offline Files
- Program Compatibility Assistant Service
- Windows Backup
- Windows Connect Now - Config Registrar
- Windows Font Cache Service
- Windows Search
- Windows Update
Although nearly all of these services have almost impact on system performance.
Some might have value that you'd miss. (e.g. PCA)
Some speed up the system compared to Windows XP (e.g. Font Cache, SuperFetch).
Some are noticeable in that you'll hear the hard-drive going (e.g. Windows Search), but highly tuned to use Windows Vista's new "background priority I/O" - so that any "real" activity always take priority over background I/O.
Beyond that, turning off Windows Desktop Composition and ClearType can help with the graphics card not being very 3D capable.