"Buy a DVD-RW drive" is a cop-out response to the specific inquiry even though it is a good suggestion in general.
"Buy a USB drive" is a cop-out response to the specific inquiry even though it is a good suggestion in general.
ISO mounting doesn't work when you have to do a fresh install or are doing an XP upgrade so it does not apply here.
Right:
LAN deployment is a viable option in specific situations.
Splitting the partition to create a bootable install partition is by far the best option. Easy, requires no spending of money, and simple to undo afterwards.