I'm sure its just called the " IT Crowd " theme, and was specially written for the show.
It's written by Neil Hannon aka The Divine Comedy. He also wrote the theme to Father Ted, which is called " Songs of Love " and DOES actually have lyrics. Check out the song, It's fantastic.
http://uk.youtube.com/watch?v=zPPi58K6wZs
He is actually mentioned when Mrs. Doyle is asked to guess the name of Father Todd Unctious.
Fr. Andy Riley, Fr. Desmond Coyle, Fr. George Byrne, Fr. David Nicholson, Fr. Declan Lynch, Fr. Ken Sweeney, Fr. Neil Hannon, Fr. Keith Cullen, Fr. Ciaran Donnelly, Fr. Mick McEvoy, Fr. Jack White, Fr. Henry Bigbigging, Fr. Hank Tree, Fr. Hiroshima Twinkie, Fr. Stick Bubblecart, Fr. Johnny Hellzapoppin' , Fr. Luke Duke, Fr. Billy Ferry, Fr. Chewy Louie, Fr. John Hoop, Fr. Hairy Cakelinum, Fr. Ebula Conundrum, Fr. Peewee Stairmaster, Fr. Tight Head Lips, Fr. Jemima Racktouey, Fr. Jerry Twig, Fr. Spodo Komodo, Fr. Canabrana Lammer
I've just realised that I've revealed myself as a Father Ted/Divine Comedy Ubernerd............. D'oh !