Ive posted these at AHT, but just as relevant here:
Here's MS student discont reg page.
http://windows7.digitalriver.com/sto...=1256355888928
Just pop in your school/college email address to see if you qualify and you can get Win7 premium upgrade edition for $29.95. That page is the US version so if youre outside of the US you may need to check what is available in your nation
Also, here's a visual guide explaining MS convoluted upgrade pathways
mtfbwya