Photoshop upgrade question

I am thinking of buying Adobe Creative Suite 2 for MAC OSX  [Creative Suite 2 :Illustrator CS2; InDesign CS2; Photoshop CS2; ImageReady CS2; Cue CS2]. It's cheap - which is what I need. I have bought a MacMini running OS X 10.8 because I got left behind on the PPC powerbook.
I understand that that CS2 is slow, as it's a half way house beteen the two Mac system architectures.
So I found a cheap upgrade [Adobe Photoshop Extended CS5, Upsell Version from Photoshop CS2/CS3/CS4]
But I wonder if this will work as an upgrade to the CS2 one. This one is Photoshop alone, so I don't know if it would upgrade just the photoshop part of the CS2 suite? I only need Photoshop, anyway [the CS2 suite is selling really cheap] 
So to be long winded... I hope it makes sense.
Thank you, anyone out there who migt know.
John
PS  There's a site selling pretty cheap Adobe products ... I wonder if anyone knows if it's a rip off site??
http://softjet.net/browse/search/?q=photoshop