Click on this link:
http://www.syschat.com/download60.html
Use some burning software like nero or ISOMagic, create a new partition on your drive, and boot from your new DOS 7.10 CD and install it on your new partition.
You can find some useful add-ons like NTFS support so that you can use it to read NTFS partitions, but remember that your new partition must be FAT16\32 for DOS to work.
When you've finished, you'll have a dual boot environment and you can choose when you want to run DOS each time you start your PC.
Regards
Martin