I too have the same case, and am about to water cool for the first time. I am thinking of putting the HD on top, in the area behind the floppy bay. There are rails there for mounting HD.
Then i can take out the HD drive cage. Should give me lots of room up front on the bottom.
The Enermax has two fans on it, and am thinking of leaving it in the normal position.
Do you think i need a fan at the top, between the power supply and the HD? IF so, blowing which way? The hd would not get much flow from that fan, as the case has a divider right below that HD spot, though i could cut part of it out. Right below the HD maybe.
Please keep me posted on what you have done, and how it worked. Or, if i beat you too it, i will post some pics here.
CYA
HEY, just found this pic:
http://www.in-win.com/icon/q500mec.jpg
My q500 has a piece of metal, from front to back where the floppy sits, and the extra spot to mount the HD is. This diagram does not have that. Does yours? Or is mine some older varity of Q500 that was different?