I've been using Vista 64 on this machine for months now. No problem with Media Player, I use it all the time. Have you run any Registry repair software? Be very creful with registry repair software, you can hose a Vista 64 registry real quick with a software that is not tested properly with Vista 64. The only blue screens I ever had on my system were due to too litle voltage supplied to my RAM and NB. A slight adjustment fixed that and I have no bluescreens ever.
You might try uninstalling media Player then do a reinstall.http://www.microsoft.com/downloads/details.aspx?FamilyID=c6a4cecb-9cb2-42f7-8814-7cb5067ee958&DisplayLang=en