You need to download and run the Windows 7 Upgrade Adviser to check if your current computer and loaded software will work with 7.
It's available free here
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=1b544e90-7659-4bd9-9e51-2497c146af15&displaylang=en
As mentioned previously there is no Upgrade Path from XP to 7.
You need to Install 7 as a new clean install and then reinstall all of your Software. Naturally you will need to apply any Windows 7 Drivers that are not included with the Windows 7 Install DVD. You will also need a DVD Drive on the computer/s that you want to move to Windows 7.
What M$ calls a Upgrade to 7 is not a typical Windows Upgrade it involves a reinstall of the OS and ideally you should wipe the HDD before starting. Though this is not necessary it is better to do a new clean install to a HDD with nothing on it so that there is no chance of any Infections or other junk ending up in the newly installed OS.
As you need to do a Clean Install of 7 you also need to Backup all your Data and this includes not only your Documents, E Mail and any Accounting Data you may have but also any Specialized Programs that store the Data in the Program not the My Documents Folder. Mostly Accounting Apps that I'm aware of but there may be others that are used domestically that I do not get involved with.
You'll also need to Backup your ISP User Name & Password as well as the E-Mail User Name & Passwords and Settings. Not to mention any On Line User Names and Passwords for Sites like Face Book or On Line Auctions Sites/Shopping/Banking.
Changing fro XP to 7 is far more complicated than previous Windows [b]Upgrades[/b] for those that stick a Install Disc in and hope for the best. However for those who always do a clean install it's no different to any Upgrade of the past. ;)
You can use Kill Disc to wipe the HDD
http://www.killdisk.com/downloadfree.htm
and other than running the Upgrade Adviser under XP there is nothing else you need do if you do not wish/need to save anything off the computer/s.
Of course if you want your Data you'll need to backup which is what you should be doing anyway.
Col