Why can't I install windows as easily as everyone says?

I have a 24" early 2009 IMac (Intel core 2 Duo 3.06GHz, 4gb ram, nvidia GeForce GT 130 512mb) that I got as a "hand-me-down" that I still payed for, thinking that I'd just slap windows on it and it'd be a regular pc... Well 6 months have come and gone, I cannot for the life of me figure out why I cant install windows!

My problem: I have a 16gb usb that I am trying to use (formatted to FAT like it says), anyway, I put the ISO into it and start Bootcamp, and it installs the drivers and whatnot from apple. when I go to click "install Windows 7" it says "the installation disk cannot be found" which I know many people have gotten before (and I've tried all of their "solutions" and none worked whatsoever)... but am I using the wrong ISO? I cant find any other windows 7 32 bit ISO's anywhere. someone please help me before I get so frustrated I explode. Also just as a side note, if I bought one of those boxes with the windows disks in it (the Windows 7 box) would I be able to install windows right off of that?

TLDR: My iMac hates me and does not want to cooperate and install windows, have tried all I have found, maybe using wrong ISO, not sure.

Thanks