Too lazy to read? Napster have quite elaborate usage rights.

Napster Terms and Conditions

It clearly states that Napster encourages you to burn old (prior to 5/2008) DRM protected content to disk or buy, the ones you really want to keep, again as DRM free mp3.

Read that as you like, but to me it seems, removing DRM for PERSONAL use is ok by them.

As long as not SONY BGM material, which they only have reseller license to, i.e. by SONY BGM terms, which means you are thrown back into the stone age of copyright law.