I dont know with GPT, I always use MBR Partition Map Scheme.
I was install OSX & Win7 on my friend's PC (Asus P5KPL-SE),
here are my workaround..
<--clicksingle HDD with 3 partitions (all Primary)
part-1: Win7 (NTFS)
part-2: Data (NTFS)
part-3: Leo (HFS+ Journalled)
[1] set active part-1 then install Win7
[2] set active part-3 then install Leo
[3] yes, it is. Win7 bootrecord will broken with this error:
[4] set active part-1 (Win7)
[5] boot with Win7 Install DVD, choose "Repair your computer" option.
startup problem will be auto-detected and prompt you to repair it.
[6] set active part-3 (Leo) again