32-Bit apps on 64-Bit Win 2003 Citrix Server

We have a custom 32 bit app written in Delphi 5.0 which we are trying to deploy on a 64 bit version of Windows 2003 Server via Citrix XenApp 5.0.

So far when testing these apps, they run MUCH slower on the 64 bit server than they do on the 32bit environment.   Is there somthing I need to do to run these apps in 32bit compatibility mode?

I need the 64bit OS environment so we can support more users on the Citrix server itself.  Obvoiuosly the degraded performance of the apps will be a show stopper.   Is there a way to issue parameters when calling these apps to get them to behave better in the 64bit environment or have the apps themselves run in 32bit compatibility mode while maintaining the server OS at the 64-bit level?