First help I can provide is telling you to learn to search the info you need for some time before asking questions without thinking.
Any of your questions could have been answered with an hour google search on the web, or some time spent reading these forums.
To replace the XP OS just install the Linux distro of your choice and when prompted use the XP partition to the Linux instalation, do not forget to leave space to a swap partition.
Linux recognizes any kind of Window$ partition ( not very sure about NTFS ), so if you have your data on a VFat partition it`s ok.
About programs, look in the net for opinions, try the programs and have an opinion from yourself.
There are too many sites so just google for it.
Any software work if compiled in the distro that is intended to work ( I think ).
"what are a few good sites to learn about using this distro?" - the official site of the distro, obviously ; and another google search...