Dell Dimension E521 upgrade from Vista to Win 7

The Vista drivers will work on Win 7.  If Dell only has Vista 32 bit, then install Win 7 32 bit.  As you only have 2GB of RAM, that is real world bare minimum for Win 7, consider upgrading to 4GB  At 4GB or less there is no need for 64 bit OS.

Win 7 will install most of the drivers needed, but it will install an incorrect sound driver.  For proper operation we have found the Dell sound driver is needed.

Run the Upgrade Advisor to see if you will have any hardware problems. You will not need vista drivers in most cases since Win 7 has most or will guide you to get them from manufacturer's web site. First thing to do is look for a bios update that supports windows 7 in Dell Downloads. Windows upgrade advisor-- windows.microsoft.com/upgradeadvisor The win 7 site also has the instructions for a clean install even if you use the upgrade disk. Make sure NOT to format the drive before you boot to the win 7 disk. It will check for vista and then allow you to format and install win 7.

Edit: There is no bios for win 7 on this older model, just make sure you have the latest bios. I would consider saving the $100+ cost of win 7 and putting it towards a new computer.

A 32-bit system will not support 4GB of RAM only ~3GB, so adding 4 is a slight waste of $. Although there are other signifigant advantages to upgrading to a 64-bit OS (granted your processor is compatible), it will allow you to break the 3GB limit on RAM. I typically run 8GB in all my systems regardless. RAM is so inexpensive today that it costs ~$40.