There's already some decent information out there on this topic, but I thought I'd share my experiences since there were a few things I wasn't expecting.
First up a caution: I am not an electrical engineer. I have no clue what I'm doing. It's possible you could hurt yourself doing this, so if you do that's your problem not mine. You will definitely void your warranty and quite possibly kill your camera if you try this yourself. That said, I managed it and I'm a muppet.
Don has some beautiful IR images of his own, one of the best being this lotus but do scroll backwards and forwards to see some others!
Lifepixel.com provides a clearer (in my view) walk-through of the conversion, and it's also designed for the G3/G5 rather than earlier generations of Powershot
A little word on the screwdrivers. You really need to make sure you've got the correct Torx driver. I found it hard to locate it in the UK, and in the end got in touch with Wiha sales who were very helpful and let me order over the phone with them direct.
The lifepixel tutorial is pretty good, but I'm going to do my own because there were one or two things that I struggled with or noticed as I was going along.
The first thing you've got to do is open the camera up. Probably best to take the battery out a long time before you do this in case there are any capacitors inside there. If anyone who actually knows what they're talking about wants to illuminate me here, go for it!
The screws you're looking for (six in total) are these ones:
Then flip the LCD screen over and remove the rear cover. Your prying screwdriver may come in handy here!
At this stage you will start to realise that the interior of a modern digital camera is a) Really complicated and b) Really cramped. Fear not - if I can do it, you can do it.
Now you need to disconnect all the cables that connect various buttons, the sensor etc to the circuit board you're looking at. What the lifepixel tutorial didn't seem to mention is that there are little plastic gates on most of these connections, so it's not just a case of brute force. The cables will come out if you just pull them, but they're a hell of a lot easier to get back in if you know this. We'll work around the board clockwise from the top left.
Top left Lift the little blue plastic bar and pull the cable out towards the top of the camera
Top right These ones are easier. Just pry them gently up off the board, and push them back down when we're putting the camera back together.
Right side Push out the little plastic gate (it's coloured blue so you can see it) and slide out the cable.
Bottom Same with these three, except the gates are brown this time.
Now you're ready to flip the circuit board out. It's a bit fiddly, and it's plugged into a socket at the bottom so it needs to come up before you flip it over to lie on top of the LCD screen. Also be careful with the cables on the left side that are still attached.
Cover Now you need to remove this strange plastic/copper cover. Try to be careful noting which bits go over and under different places! You need to remove the marked screw before you slide it out.
Now we've got down to the back of the sensor. If you can find a way to keep all the cables out of your way while you work, it'll make your life a bit easier.
The sensor itself is held in place with 3 Torx screws. We need to take them out! It's also a good idea to flake off as much of the blobs of glue that are dotted around as you can - but be careful!
Now lift the sensor out carefully, and watch out for the focus spacers (basically really small metal washers) they may be glued down, but one of mine went walkabout inside the camera. As you can see in the picture I also knocked one of the springs on top of the filter. Like I said, I'm a Muppet.
We've finally got down to the thing we're interested in - the filter. It'll be glued down, but you should find it fairly easy to pry it out with a little screwdriver and some tweezers. Try going around the edges to loosen it before you flip it out.
Then clean the new filter thoroughly with the lens cleaning solution and drop it into place, making sure it's seated in properly. lifepixel suggest using silicone to cement it in place, but I didn't bother. We'll see if I live to regret that or not!
Basically just retrace your steps.
The most fiddly thing of all was getting the *&^!ing focus spacers to stay in the right place. In the end I used a tiny dab of superglue to hold them in the right place on the underside of the sensor bit. It goes without saying you've got to be really careful not to put fingermarks/glue/etc onto the sensor itself!
When I'd put it all back together I found that some of the buttons didn't work. I hadn't quite pushed one of the cables all the way home, so take care with those. But don't worry - you can always open it up and try again.
And just to prove it works:
There are some more shots from a recent excursion in the gallery