Ok, I only use Win 7 part-time (I boot 4 different OS's), and I did not remember exactly what I did to access my XP partition.
The following should work for you (you do not need to be in safe mode for Windows 7).
Open Windows Explorer in Windows 7, right-click on the XP partition, choose Properties, then the Security tab. Under Groups or User Names, you should see several listed. Look for Administrators and Users.
If you are missing either one of theses, click on Edit > Add, and type Administrators in the box and click on Check names. Something like "DJCHAD-MAC\Administrators" should appear. Click on OK, then click on Add again and type Users in the box and click on Check names. Something like "DJCHAD-MAC\Users" should appear. Click on OK, OK, and OK. Now open the Security tab again (if you added Administrators or Users)
Click on Edit, then highlight "Administrators" and check the box for Full control. Next highlight "Users" and check the appropriate boxes (I have the "Read & execute", "List folder contents", and "Read" boxes checked). Click on OK and OK.
You can also do the above for specific folders instead of the entire partition, if you do not want access to the entire partition from Windows 7.