the site is in the westwood college building on the SouthWest corner of Cumberland avenue and Higgins avenue; which is 1/2 block north of the cumberland blue line stop for the "L" train.
As such, there are several options - stay at the o'hare hilton; stay at one of the hotels on river rd. in rosemont (which is the blue line stop between the airport and cumberland).
final common pathway 1: catch the blue line, get off at cumberland and walk a 1/2 block north.
final common pathway 2: cab from rosemont (higgins & river) to site (cumberland & higgins) = 1-2miles = ~5 bucks.
another option is the holiday inn on higgins 2 blocs east (with a Hooters inbetween the hotel and site), the amerisuites on higgins 3 blocks east (with an outback steakhouse in the 1st floor) or the clarion 1.5 blocks south on cumberland. the clarion would be my choice, b/c when it was a mariott, they found OJ's bloody knife in the woods behind it... no joke. =)
I grew up 1 mile away from the test site, and know the area quite well, so feel free to PM or ask questions. CS is a paininthe*ss, but is ultimately just another hoop. good luck.
-t,md