I think you need Crystal 11 to do dynamic parameter fields.
Don't know if it's supported in 7.3.
So Crystal reports 10 can't do linked fields, I would consider this as a staple feature that should have been included from the word go, static lists are not very useful when you have 100's of items which are related to specific customers.
I may have to ditch crystal reports and do a web based version of this report using PHP and SQL as crystal cannot even cater for this simple and basic task.
Many thanks for the reply, I'm just a little gutted because I just cant believe that the product does not support this from the outset of it's conception as it's a relatively essental need even back in 2003/2004 when crystal reports 10 came out.
It looks like noone knows the answer to this issue, if anyone has any idea how to do this please reply.