You can now download the free OSTN02 transformation tools for ArcPad 7 and ArcGIS 9.1.  To download it you need to log in to http://www.myesriuk.com/esriuk/members/downloads.asp.  Its listed as OSTN02. 

obviously you need to be registered with myesriuk.com to do this.  The download adds a new transformation to ArcMap that you can use when using OSGB36 based data It  also has an installation to support OSTN02 in ArcPad 7.