A hex editor is actually a lot like a text editor/word processor. Except that you are viewing/editing files as hexidecimal numbers, which lets you see/modify pretty much any file on your computer. It also may show things in text, if the file contains text elements.
If I understand correctly, you are wanting to convert a .pak file into a .set file and some .map files? This is very very simple with a hex editor. All you need to understand is load/save, cut/copy/paste/delete, and find/search, all of which you've probably done before unless you have never used a word processor.
So, if you haven't already, find yourself a hex editor. I use one called "Frhed". It has a few quirks, but it's free.
First a bit of info about a .pak file:
A .set file is always 842931 bytes. The first 842931 bytes of the .pak file are the data from the .set file. Somewhere within those 842931 bytes will be the word "MAPS". This is probably left over from an earlier version of the game when they put the map data in the .set file, so ignore it. The second time "MAPS" shows up in the file will be at byte 842932 and this will be the start of the actual parent city .map data. If there are no colonies, the map data goes to the end of the file. Otherwise, the 3rd "MAPS" will be the start of the first colony, the 4th "MAPS" will be the 2nd colony, etc.
Okay, so
1. Load the .pak file into the hex editor.
2. Find the 2nd time "MAPS" appears in the file.
3. Use your editing skills to put everything before the "M" in "MAPS" into a file called (Adventure name).set.
4. Then put those the "MAPS" and everything after them till the 3rd "MAPS" (or end of file) in a file called (Adventure name)P.map.
5. If there are colonies, put the maps in appropriately named colony files. 1st colony is 3rd MAPS till before 4th, 2nd colony is 4th MAPS till just before 5th, etc.
Here's what the area near the "MAPS" looks like in a hex editor:
0cdc80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................................
0cdca0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4d 41 50 53 41 01 00 00 21 00 00 00 00 ...................MAPSA...!....
0cdcc0 00 00 00 44 bd 63 00 04 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 b0 c8 f9 00 04 00 00 00 01 ...D½c.................°Èù......
0cdce0 00 00 00 00 00 00 00 00 00 00 00 b4 c8 f9 00 04 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 40 ...........´Èù.................@
0cdd00 b1 f9 00 14 00 00 00 2c 01 00 00 00 00 00 00 01 00 00 00 38 bf d4 00 04 00 00 00 10 cb 00 00 00 ±ù.....,...........8¿Ô......Ë...
0cdd20 00 00 00 01 00 00 00 28 f4 d3 00 01 00 00 00 10 cb 00 00 00 00 00 00 01 00 00 00 98 d0 cc 00 04 .......(ôÓ......Ë...........ÐÌ..
The leftmost column is the number of bytes into the file, in hex. For example, if you put "0cdca0" into a scientific calculator (windows has 1 under accessories), you get 842912. Each pair of characters in the middle area represents 1 byte as a 2 digit hexidecimal number. There are 6 lines, each with 32 pairs, so that is 192 bytes. The area at the right shows what the data looks like as ASCII text, if it looks like anything. "4d 41 50 53" corresponds to the "MAPS" text.
Hope this made sense.