Debian: There are several versions of Debian, I suggest that your best choice is likely to be Etch (aka testing, although it's due to become the new stable as soon as the developer finish their latest fude). If you have a high speed connectoion then I suggest that you do a net-install rather than downloading and burning one or more full CDs or even DVDs, you can get the ~100 meg net-install ISO here. Be sure to get the flavor that you want, for most pc users this is i386, but if you have a new fancy 64 bit computer there are Intel and AMD versions for the 64 bit cpus too (as well as versions for other computers). I usually burn it to CDRW since it may change and you may need a new one soon (this was expected to happen Dec. 4th but Debian never seems to hit announced dates). The installer will offer to erase your disk or to use unpartitioned free space on the drive (it can't use remaining space if that is already taken up in a partition). When you get to the type of system to install (many minutes into the process) be sure to select the desktop option, assuming that you want a GUI. This will install Gnome, you can install kDE later, if you want it, with apt-get. Be sure you make note of the account name that you create as well as the passwords you assign that account and root. Good luck and have fun.

As to saving to a usb device: I don't do it, I'm one of the users who made a FAT partition. And I've only used that for compiling some programs. But if your flash device is FAT partitioned (most are), plug it in before booting and you should be able to see it on your desktop when you boot. (maybe named something like SDA1). See answer #6 for details on how to make it writeable (the default is read only). You should be able to then drag and drop any file you want between the flash drive and ram disk, or use the full path of the partition when you want to save something. Of course, once you have Etch installed this will not be an issue.