Computer Techy Help part 2 required please.....

I currently run XP on a machine I bought from Dell some years ago, which came with an OEM version of XP. I am considering buying a 120Gb SSD but want to know if I can copy my operating system onto the new SSD and activate it using my OEM licence key?

Failing that, would I be able to buy an upgrade version of Windows 7 and use the same XP OEM key to activate? (I'd rather not have to fork out for Windows 7 on top of an SSD in all honesty, as the main thing attracting me to an SSD is the current cost. If I have to buy Win7 on top of that it kind of defeats the object).

Thank you.