I'll try to answer what I can.
1) Is a DD 5.25" disk used in 360kb drives, and is there a HD for 1.2mb??
For the PC family of computers there were two
MAIN formats for the 5.25" drives. On XT and earlier, there were DS/DD drives (and SS varients) that supported up to a total of 360k per disk. On AT and later, there was DS/HD, which supported 1.2m per 5/25" disk.
For the pedants, I know there was also the 160/180k single sided formats and the 320k double sided formats. I think there were several others, including the DS/QD (720K 5.25") e.g. Tandy 2000, but I'm trying not to be too confusing.
See:
http://www.apple2.org.za/mirrors/ground.icaen.uiowa.edu/MiscInfo/Misc/diskfmts for some great floppy format details. Those marked (3) were PC, (4) were introduced in AT and later.
2) Is 360kb on a DD DS disk 360k on each or in total?
Not sure what you're asking. Each diskette held 360k total, or 180k per side.
3) Anyone know where I can find any information about the 4 DIP switches on the back of my XT clone? I want to know what they do.
See if the board is listed at:
http://www.resoo.org/docs/_hardware/th99/m/m8088_1.htm
Don't just search by name, but look at the different board layouts.
4) Does the XT support 1.2mb drives, and is it likely my clone will?
Not natively. There are add on cards that support 1.2mb and 1.4mb drives in XT class machines. These have their own bios. These are still available from
http://www.jdr.com/interact/item.asp?itemno=MCT-FDC-HD4
I have several of these in my duplication machines at home to support different formats.