Ok, as you say the disc is full, and as long as the disc continues with less than 80Mbs of free space you will get that pop-up message.
What to do ?
You could disable diskclean reporting on that disc, but that involves a registry hack.
You could burn a lot of the disc contents onto CD or DVD and then delete the same off that drive I freeing the space.
You could remove that I drive ( if it is a seperate HDD and not just a partition of another HDD ), and put it in a usb caddie as an external drive.
Or........the simplest way...........buy a usb connecting external hard drive, plug it in, copy all the files on the I drive onto that external drive, make sure that the files have copied succesfully, then wipe the I drive...and bingo, files safe on an external drive and the I drive now empty and ready for more pics.
External hard drives are cheap.....as an example have a look at these
http://www.ebuyer.com/store/Storage/cat/Hard-Drive---External ........they are a doddle to use, and I am sure that if you went down that route you would find all sorts of help here in getting up and running. Most external hard drives on XP don't even need extra software..just plug in and play.
edit to add..........Your existing I drive holds 33Gbs (about).........buy one at 250Gbs or 320Gbs capacity for less than £40 and it meet all your storage needs and more.