The Linux distros could also be interfering. Always best to have OS's on separate HD's booted via BIOS to avoid interference. If not GRUB should be installed last after Windows 7 to a wiped HD: Where to install ubuntu in my system?
Do the Windows 7 disks provided include a Windows 7 Installation DVD? If so, boot from it to do a clean install after formatting the Windows 7 partition first: Clean Install Windows 7
You do not need to reinstall Vista first, as the DVD will scan system to see any OS and allow use of Upgrade version key.
If there was formerly GRUB on the Windows 7 partition, wipe it first using free Partition Wizard bootable CD to Wipe from the Disk tab. You may need to do a workaround to clean install Upgrade version Windows 7 to wiped partition: Clean Install with a Upgrade Windows 7 Version
The installer is mostly driver
-complete, with newer arriving quickly via optional Windows Updates. Any drivers
then missing in Device Manager can be found on the Dell Support Downloads webpage or driver CD if provided.
Install updates and then programs slowly over time to gauge performance after each. Don't let any programs write themselves into msconfig>Startup as they become freeloaders on your RAM/CPU and can spy on you. I only allow AV and gadgets.
Use a lightweight free AV like MS Security Essentials which works perfectly with Windows 7 Firewall.
When it is finished, clean and order the HD perfectly using state-of-the-art free CCleaner then Auslogics Disk and Registry defraggers monthly.
Then save a Windows 7 Backup image externally so you never have to reinstall again, just reimage the HD or replacement using DVD or Repair CD.