windows 7 MS office....

Hi! im am planning to buy windows 7. i currently have vista installed and i have ms office 2007 professional installed. I have used all three times of serial keys that come with it. if i do clean install of win 7, does it wipe all programs or just the files? since i dont have any legal ms office 2007 keys i want to upgrade but does it mean that i have to buy another ms office 2007?

This is not a new or fourth computer - you are just upgrading the operating system for that computer. You can legally use the same key you have on this Vista system. You have 3 keys, you can use them on any 3 computers you own. What you can't do is install Office on a forth machine - you would have to uninstall it from another first. The licensing rules are a bit different for applications (like office) and operating systems (like Windows).