The HP210 will have twice the resolution of the ipod Touch which will give a clearer picture with more detail. (i.e. The HP210 screen will be better)
The ipod Touch comes with up to 16GB of (nonexpandable) flash memory built in.
The HP210 won't come with much built in, but with 2 memory slots you can expand the memory as far as your budget will take you. For example you could put in a 32GB CF for $160 (
Newegg.com - A-DATA 32GB Compact Flash (CF) Flash Card Model SPEEDY CF 32G - Retail) and a 16GB SDHC for $80 (
Newegg.com - A-DATA 16GB Secure Digital High-Capacity(SDHC) Flash Card Model TurboSD SDHC 16G - Retail). This would give 3 times as much memory as the iPod Touch.
You will be able to swap out memory cards on the fly to further expand your memory in the HP210.
When larger CF or SDHC cards are made you will be able to add more memory to your HP210.
You will need to buy a new iPod Touch in order to upgrade its memory.
The HP210 will have a user replaceable battery allowing you to carry multiple batteries or replace an old failing battery. The iPod Touch doesn't.
We don't yet know what battery life on the HP210 will really be like when watching video's or listening to music, but for a single new battery, the iPod Touch will probably be better.
The iPod Touch has a better user interface.
The HP210, with free add on software like TCPMP, has much much better CODEC support.
Speaking of add on software, there is really no comparison. the HP210 already has many many many programs available, many of them free. The iPod Touch may have some someday. This makes the HP210 much more flexible.
The web browser on the iPod Touch is probably better than anything available for the HP210.
The HP210 will be much better at PIM as an organizer.
You can do much more with an HP210.
The iPod Touch "Just Works"
For your usage case though, I would recommend looking at an HP310 also. It has a better screen than either of these.