After thinking about it for a couple of days, I just went out and bought an iPaq. Then I went along to my friendly local chess shop and ended up buying not only Pocket CT Art and Pocket Fritz, but a couple of other convekta programs as well ... Pocket Chess Strategy and Pocket Chess Endings. I thought I might as well while I was there.
Chess Strategy and Chess Endings are almost exactly the same format as CT Art, but with different problems. I've had a bit of a play with them, but not that extensively. I'm still planning to mainly focus on CT Art. Chess Strategy feels different because there is not really a definite 'checkmate like' solution, so it is more vague. Fun though. I completely can't identify good moves to exploit weak squares though! ... the only theme I've explored so far.
Pocket Fritz is good, although it was very difficult to install. The standard out-of-the-box install program didn't recognise the newer Window Mobile operating system, and I had to hack around using a patch update installer from the chessbase website. Got there in the end though.
Pocket CT Art definitely does the job, but is a cut down version of the PC edition. There is no 5x5 help board if you go wrong, and you can't play a position against Crafty in practise mode. I would recommend using the PC version initially, and use the Pocket PC version for practise on subsequent circles.
There is a bug in CT Art though - selecting tactical themes from the drop-down list doesn't properly work, and the number of new vs solved exercises is wrong. Playing a practise game first in the themed mode solves this.
I've started my 5th circle on my Pocket PC now. I completed level 20 on my PC in my 4th circle, and then decided to start from scratch again on the Pocket PC.
I whizzed through level 10, and I am progressing swiftly through level 20 and have completed about 70% of the problems. Level 20 is becoming a lot easier and I'm solving them in less than 1 minute on average. So I can sit down and do 20 to 30 in a session. However, I can still only dream of doing this for the level 90s! Maybe one day ... or more like maybe one year!