A couple of things:
1) There is a Mac version of Picasa. You can move your pics to your new iMac and keep using the program you use (and I assume, like). iPhoto is pretty sweet, though; but I believe that I actually prefer Picasa on my Windows 7 PC to it (haven't fooled with Picasa on the Mac too much, as my MBP is my "work" computer).
2) If you only have one document that you're needing to use the spreadsheet for, you've got two decent options. First, OpenOffice is free - try it first, obviously, before you pay for anything. If that doesn't cut it, try Apple's Numbers spreadsheet program - its $19.99 in the Mac App Store. [Is there a free trial available? There used to be...]
Have fun and enjoy! But be prepared to buy another... and another... that tends to be the way it goes.

BTW, we're a family of three (well, almost; baby girl will be here in August) and we have the MBP, my Win7 desktop, two iPhones and an iPad. And the sad part is that that doesn't even begin to compare to some of the others here...