My drive is partitioned into several logical drives - if I install onto C I presume the others will be left intact? It doesn't insist on formatting the whole drive?
Tell it to go to partition C, then that's all it will touch. The rest of your stuff will be safe, don't worry.
As far as 64-bit goes, there's no sense in looking at 64-bit windows if you are running under 4Gb ram. Also, I believe you do need a 64-bit processor for 64-bit windows so if you don't have that with your laptop (you don't tell us the model) then there's no sense in considering 64-bit Win 7.
Oh, one last thing. Personally, I don't think it's worth getting any version of 7 below "professional" and am running "ultimate" on the desktop PC (can jump between English and Dutch seamlessly on demand, something you cannot do with anything below that level). That's just my own personal thought, nothing more.