|256MB RAM is not enough for running Windows XP.|
XP requires 500MB RAM or more if you plan in running up to IE6 or 7, and more than that if you plan on running IE8 (But I would not recommend that on a P3 anyway)
A Pentium 3 IF it could be installed would run XP very slowly.
The existing partition tables on your hard drive are obsolete, you would need to choose Custom and Partition on the install and delete all partitions and create a new partition and format it.
6GB hard drive is not enough for installing Windows XP on, it requires more than that for itself. If it is going to work, you would need at least a 40GB or preferably an 80GB drive to leave room for some programs and files.
Your machine should be running Windows 95 or Windows 98 or a Light version of Linux if you expect to be able to just surf the internet and emails and possibly a few older software titles.
Personally, I would not bother with hardware that old.
You have to be a little bit crazy to keep you from going insane.