I was thinking of doing something similar, but into the side of my Antec Sonata III case. This shiny box (which I picked up for £65 in a sale a few years back, including the 500w Earthwatts PSU!) was fine for my previous build, but since I upgraded to an i7 950, GTX460 and replaced the (now dead) Earthwatts with a Corsair TX650w, the cooling is pretty dire, with no intake fan whatsoever.
That 140mm radiator grill looks like it would do the job, and I'd couple it up with a Sharkroom Silent Eagle
http://www.overclockers.co.uk/showproduct.php?prodid=FG-009-SH
Trouble is, though I'm keen to crack out my drill and jigsaw to have a go, my DIY skills are somewhat lacking, and I'd be wary of messing it up, especially considering the glossy paint finish of the Sonata. Last time I tried to mod a case, I ended up drilling holes in my landlord's kitchen table. Doh!
Also, the fan and grill comes to almost £20 with postage, and I'm thinking that if I just spent another £20 or £30 I could get a more suitable case, such as an Antec 300 or, preferably, a Zalman Z7, and not have to worry about drilling and cutting into the shininess of the Sonata (which I could probably flog on fleabay for a decent amount, even without the original PSU).
Decisions decisions.