[Is it possible to wear both bought hair and a hat at the same time ?]

Right click the hat in your inventory and select attach to, then use your chin ( if you use your nose you can not wear glasses) and attach it. Then right click the hat on your avatar and adjust it until it is in the correct position and rotation on your head. Viola, hat and hair at the same time. Since it remembers the attachment point, you should only have to do this once, from then on, you just wear it.

[Can not login to Aditi (Beta Grid)]

I can not log into Beta Grid either, I get the same ' Login Failed - Unable to connect to Simulator '  error. Not sure why some can log in and others can not.

[Win 7/ Vid card help]

I would try reinstalling the NVidia drivers. Make sure you have the latest from the NVidia site. UNinstall the existing video drivers under control panel > software. DO NOT just install over them. Then install the new drivers. I am running Win7 and NVidia and have no issues.

[Rectangle-help]

Easy to do, Wear, Attach To and Attach to HUD are very close on menu.