I suggest incorporating some of your player functionality into it as well, so as well as a "launch Audiosurf" there's a "play track".
I prefer to leave YAAP and ADC seperated, I could add 'Play song when finish downloading' or something like that, but it's the only one I can think of adding... I don't want to end with a mix of both programs, and I think also that ADC it's kinda bloated atm, so maybe on future versions I'll start removing some useless things...
To just play a track you don't need to register with the window, just send the play info so it should be considerably less complicated to add.
Are you sure you don't need to register the window? =S
Also I noticed you're using steam://run/12900 to run Audiosurf, I instead grab the Steam.exe location from the registry and run that with the parameters -applaunch 12900 using Process.Start(). Not sure which is better, but grabbing the location of the Steam executable will also allow you to locate Audiosurf and drop the .ash file into the relevant directory as well so will be worth doing from that perspective anyway.
The code is in Audiosurf Prodder or I can paste it here if you want a look (I'll even drop it into VB for you
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I use steam://... because I think it's some kind of way to be 'sure' that it's not a pirated version of Audiosurf, at least if it IS a pirated version, you lose the Launch button

As for the .ash file, I thought I could add a 'Set where to locate the .ash files', like the download path but with the .ash...
Oh and glad to see you on the scoreboards, Mincus hehe