Using a Dell XPS420 desktop. I checked my hard drive partitions, getting ready for Windows 7. I found 3 partitions: Windows (C), Recovery (D) and EISA. Should I delete EISA and recovery, before I attempt a clean install with the 7 upgrade disc?
I prefer that I have only one partition after upgrade.
You can install Windows 7 in the partition you want it installed in or you can modify the current partition structure but Windows 7 doesn't create a recovery partition.
The EISA partition is the Dell Diagnostics Partition. You can boot Hardware Diagnostics with the F12 boot menu.
The D:\RECOVERY partition holds the image of the system as it was shipped to you.
You can delete either or both. If you don't want that hidden diagnostics partition, you can download the same Dell Diagnostics from Dell's Drivers and Downloads site and create a bootable CD or USB stick with the Diagnostics.
If you delete D:\RECOVERY, you will lose the ability to restore the system to factory shipped (Vista) conditions (Vista and any software you purchased with the computer). Installing Windows 7 in the current C:\OS partition will remove the automated F8 factory recovery option but the factory image can be restored manually as long as the partition is still intact.
Having the D: partition doesn't hurt anything and you can even hide it if you wish. Having your original Vista installation available and deployable in about 15 minutes might be handy for any warranty work, troubleshooting, or whatever.
You can have up to 4 primary partitions so you could keep both the hidden EISA and the D:\RECOVERY, install W7 in the current C:\OS partition
and create another partition for backups if you wish.
Lastly, at a minimum, if you really wish to clean the hard drive and delete the recovery partition, you might consider copying the whole D:\RECOVERY partition (probably around 9-10GB) to a backup drive, USB drive, etc. The partition could later be copied to any hard drive and the factory image could be manually deployed (I could help you with the details if necessary).
Tom