How to set file numbering to specific value?

I have an XTi. I put my memory card in a store's 40D and obtained some sample pictures, then put them in my camera and uploaded them to my computer using the camera. I later took a few pictures using the card. I was using continuous numbering, but the numbering in my camera went haywire, and I found out when I downloaded my pictures.

My last pic before putting the card back into my camera was IMG_4575, and after that, it was IMG_7934. I tried manual reset but it went to a new folder. Then, I took both batteries out, and put a memory card with the correct folder and the last correctly-numbered picture in the camera, thinking it would do the trick! But no, I've got pictures in folder 102 now, instead of 100.

Anyone know how to reset the numbering to use folder CANON101 and file IMG_4576?

I think I figured it out. It's annoyingly complicated.

Canon actually orders pictures by foldernumber*1000+pict​urenumber. The camera will update its continuous count if foldernumber*1000+pict​urenumber is greater than what is stored in the camera's flash (the memory flash, not the light flash). This data, like the deadpixel removal data, is nonvolatile and will persist even with both batteries out. (Incidentally, I would imagine that this is how they get the shutter count.)

So what do you do? You need a card reader.
1. Make a folder named DCIM\CANON999 and make a file named IMG_9998.CR2 or JPG (I used CR2). The camera should warn you that it can't make any more folders when you turn it on.
2. Take a picture and verify that the camera has recorded IMG_9999. The camera should now complain that you need to replace the CF card.
3. Instead, format the card. (I can't recall if I did a manual reset now...) We should be back to folder 100 now, file IMG_0001. Take a picture to verify.
4. Move the card over to a computer. Remove everything except the CANON100 folder. Rename IMG_0001 to IMG_xxxx and CANON100 to CANONxxx of your liking.
5. Put the card in your camera and turn it on. The new numbering should be in effect now, but take a picture just in case and make sure that it's working as it should be.