The "366" models are the 366 GX1 version. They usually ran WIN CE and could have 256mb of RAM. They have USB1.1 ports. Lots of reading on the forum for you with those models. They can run Puppy Linux or some version of trimmed XP (MicroXP, XP-Lite, etc) - you can also role your own lite version of XP with a tool called NLITE from here: http://www.nliteos.com
The 360 is the one with the mPCI slot that the WIFI card uses. They have the more powerful LX800 processor and USB2.0. Usually they have 256mb or 512mb but sometimes you can find them with 1gb of RAM. This is the more powerful of the three and can run WinCE, Linux or XP Lite flavors or XP Embedded. Lots of reading here too on the forum. The 360 video supports rotation - nice feature. The GX chipset on your 366 models does not support rotated video.
The D=PAD or directional pad is for reproducing the arrow keys. For mouse-type action you would use the touch screen. All three have bluetooth too.
Modifications are tough and hard to tell what someone did - that will be a challenge.
Getting into the BIOS is easy, plug in a USB keyboard and tap the F1 key as you power up. The BIOS battery on the 360 is obvious and on the 366 the battery is under the 'jumper board' on the right side in the pictures. Carefully pull it staight up - do not pry one side as the pins bend easily and then break off when you try to bend them back. The battery is under the mini jumper board. They all use the same battery. Note the cut edge orientation so you can but the board back in correctly.