Must be a P4 or above at that frequency. If you are lucky it's a dual core, and if you are luckier it could be upgraded.
Min. RAM requirement for Win 7 is 1GB, realistic min is 2GB, and a recommended minimum is 4GB. If the PC can't support 2GB RAM it's inadequate.
HDD of 100 is fine - for a system disk. Just add another data disk.
Graphics are likely to be a bit sluggish, too, so might need upgrading also (particularly if it's an embedded GPU).
But by the time you've identified and sourced the components required to upgrade, plus the Windows licence, you would be a good way towards buying a cheap but current(ish) spec. PC.
Going from Win XP to Win 7 is pretty much the same sort of jump as to Linux Mint, so might be worth trying Linux on the PC if it isn't quite up to Win 7 (unless there's applications that he needs that are Windows only).
SD