Windows file systems do not understand the Linux permissions scheme.
If you are installing Linux as the only OS, you should delete existing partitions and repartition the drive, then format the partitions to a file system that understands the Linux permissions system. If you are installing it along side of another OS, you will need to resize at least one of the existing Windows partitions, then repartition and reformat the newly-created free space to receive the Linux install. Many--not all--distros' installation routines will offer to do these tasks automatically or almost automatically.
Back up any crucial data to external media before mucking about with partitions.
I just checked the specs of the Dell Dimension 2400
. Most Linux distros should work with it, but I notice the base RAM was just 512 MB. If you can, it would be good to max out the RAM to 2 GB. Otherwise, you would do well to avoid using heavier desktop environments such as Gnome, Ubuntu's Unity, or KDE. I have a Dimension 4400 with 4 GB RAM and I'm running Debian Wheezy (v. 7) with the Fluxbox window manager, and it performs quite nicely. I'm running Fluxbox because I like it, not because I had any difficulties with the default, which is Gnome.
You can install a distribution that defaults to a heavier desktop--that's no problem. Just plan to install and use a lighter one, such as LXDE, unless you up the RAM significantly.
As for recommending a specific distro, it's like asking about cars. A Ford guy will recommend Fords, a Chevy guy with recommend Chevies, a Chrysler guy will recommend Chevies, etc. I'm a Slackware guy. I'll recommend Slackware.
I would suggest you burn some Live CDs
of distros you are considering, boot to them and play with them for a while, then pick the distro that seems to be a good fit. I would also suggest sticking with it for at least three months until you have gotten some of the hang of how Linux works before deciding to try something else. The LQ Download Linux page
contains links to the most distros.
I would recommend against Fedora--it's kind of bleeding edge. Mint, Mageia, SalixOS, Debian would all be good candidates, just to pick some from thin air.