OK Here goes:

I have just played the demo of NFS on my XP Box (and now I know why I never bought the game LOL)

I should point out however that I reformatted my Hard-Drive long ago as FAT32 and not the standard NTFS as most XP machines will be. The reason being is that DOS wont recognise an NTFS Drive.

1) Get a good DOS Boot Disc (http://community.the-underdogs.org/pub/bootdisks
/)
2) Save or copy the game to a folder on your root directory (c:\NFS) (only on FAT32 systems. If your system is NTFS then you need to install the old DOS game to a folder (as above) and then rip that folder to a CD
3) Ensure that the details of your CD Drive are on the Autoexec/config files so that it runs from the DOS boot disc (ie, :
rem *ENTER YOUR OWN CD-ROM DRIVER HERE*
example: DEVICE=C:\CDROM\NEC_IDE.SYS /D:NECCDO
4) Put the DOS Boot disc in your floppy drive, and reboot the PC in DOS
5) Navigate to the C:\NFS and execute TNFS.EXE (or on an NTFS system the CD Rom: D:\NFS\TNFS.EXE
6) BINGO you have a chunky graphics, rubbish sound and rather bland game of an era long since surpassed 