Dos based Programs under WIndows XP

In the last year, our company switched to using Windows Xp as the O/S on user PC’s. However, 3 users access a Dos based program, written 15 years ago, and they all have experienced that XP has slowed down their response time in the Dos program. The Dos program resides on a Windows 2000 server and is predominantly a data base.
I read with interest the article “Tweaking performance under XP” and wondered what would be the ideal settings for these users who pretty much do not use any other programs, except Outlook for email.