this is a perfect example of why buying music online is totally uncomparable to purchasing an actual physical CD you own and the price should reflect this but doesn't.
DO NOT let windows or any other program run a scandisk or anything else on that drive. U said it happened after he rebooted - lets hope it didn't run scandisk when it rebooted.
You cannot let anything touch this drive as they will all try to 'tidy it up' and clean up the partition info, fat table, etc. etc. to what they think it should now be (an empty drive) and this will mess up the files that you are trying to recover even more.
As for the music you purchased online, u could try contacting the sites of the people u purchased it off. Give them your payment info, tell them the situation and if you got lucky, one of them might possibly be able to offer some way for you to get the music again, but I wouldn't hold my breath for that.
For all stuff you ripped personally I'd say re-rip it. 'Recovered' music in my experience is not the same again and just isn't worth the time to recover (its as fast to re-rip an album as it is to recover it except re-ripping it gives you perfect quality).