A PDA or PDA/phone would do everything you're looking for except connect to a USB stick and edit powerpoint.
Any one of the Ipaqs we sell has windows mobile 6 so you get outlook built in as standard for all your contacts calender and tasks. Internet explorer is also built in along with pocket office so you can open and edit word and excel. powerpoint you can view but not edit. Image viewing is also built in and all of our current systems have bluetooth so they would would connect to the GPS receiver.
Arcpad I've never used but it runs on your friends PDA it should run on any of these.
http://www.totalpda.co.uk/HP/HP-iPAQ...cc549a6c6be374 http://www.totalpda.co.uk/HP/HP-iPAQ-214.6975.html
If you want a normal good spec PDA thats meets most of your requiremetns get the 114.
The 214 is slightly higher spec but the biggest difference is the bigger and higher resolution screen. You will see the benefits of this if your doing lots of documents, spreadsheets and Images as its twice as sharp as the 114.
For a PDA phone you can look at these 2
http://www.totalpda.co.uk/HP/HP-iPAQ-614.6976.html http://www.totalpda.co.uk/HP/HP-iPAQ-914.6977.html
These are both both pda phones with a slightly lower spec than the two above. They both have the same windows mobile 6 and wifi and bluetooth so still meet all your requirements. There unlocked so can use any network and both support 3G and HSDPA for faster internet access.
We also have ruggedised models.
http://www.totalpda.co.uk/Ruggedised-PDA.10033/
Similar specs and sizes to the models above but along the lines of the toughbook you already have.
Give me a call if you have any questions.