Am having similar problems getting MP client to run from resume from sleep, for me also it's not the PC that has froze, just MP. Have also tried closing MP before powering to sleep, resume and OS is fine, launch MP but it will freeze and have to kill it. Note i don't even get as far as the UI to try TV, Videos or anything. So I am thinking it's an OS issue and will probably do a clean install. You mentioned 'upgrade to Windows 7' or was it a clean install.
Am only just starting this project but this is the only real stumbling block I have.
I have also been following this thread, where other people seem to be having similar problems. On Monday night I unchecked anything to do with EPG grabbing and sent the PC onto standby. When I arrived home last night I resumed from standby and it worked! A little too early to claim it is now fixed, but I'll carry on testing this over the next few days and report back here.
@vic - I only have the upgrade disc for Windows 7 so I wiped the PC clean, installed Vista then immediately upgraded to Windows 7. So I would count this as a clean install.