Mine was done by MaxMax.com in the US. There's also Lifepixel.com and various other places. Lifepixel also sell do it yourself kits, though I have never tried this.
Remember you can do great images with an unconverted camera too, just your exposures will be long and so there are many types of photography you can't do. If you look at the other infrared articles on my site you'll find lots taken with unconverted cameras. There are also RAW files you can download to see what you'll get and experiment with processing them.
I really love the look of some infrared photography and one image about half way down your page, which measures 21989 x 855 pixels is the kind of look I want to experiment with. Really beautiful colours and look to it.
Who did you get your camera converted by?