Apparently, a rapper who calls himself Poverty wrote it in 2006. From a782008's YouTube page:
GARTH DID NOT WRITE THIS SONG
HE IS A FRAUD! The song was written and recorded by an artist known as Poverty who is a rapper. His myspace is myspace.com/poverty. He was a song writer for crazytown. He wrote rock songs and rap songs and that was his voice on the track when Garth was singing over it. Garth used to hang around Poverty a lot back in the day and he asked for a copy of the song saying "he liked it." then 3 years later he is brazenly singing over his voice on national TV and claiming the song is his.
I actually kind of like the song.
But this is interesting. Garth the Plumber used to hang around with Poverty and crazytown (if you follow the link to Reality Roll Call, you will see a clip of Garth the Plumber singing "Sex Mode" to Mary Carey on "Celebrity Rehab with Dr. Drew" [he was in the treatment center visiting Shifty from crazytown]). I guess I'm still naive, but I thought that Garth the Plumber was, well, just some plumber who auditioned for Megan's show because he was interested in her.
But, if he's been on a previous VH1 reality show, maybe he was recruited by the producers. Which, of course, throws into question the entire enterprise.
How many of the other contestants were recruited in this manner? Will footage turn up of Al on Charm School with Sharon Osbourne?
Oh, doubt! Oh, questioning! Oh, misery!
UPDATE, a little later in the day: Now I've spent entirely too much time thinking about this, but-- wouldn't the producers of the Megan show have had to get permission from the rights holder to show Garth singing this song? If Garth claimed the song was his, then he would have just signed the release himself, granting producers the right to use footage of him singing the song. That would be fraud.
If, however, he was honest with the producers, and told them that he didn't write the song, then the producers had to get permission from the rights holder (possibly Poverty). In which case, it's the producers who have committed the fraud, by letting viewers believe the song was Garth the Plumber's.
The fact that Garth has appeared on another VH1 reality show, along with a member of crazytown, a band for which Poverty apparently has written some songs, makes the whole issue even more convoluted and suspicious.