Help please: Client Custom Field

[hushz]

Can someone pls give me some advice on the following:

 

When a visitor clicks on my link http://www.mydomain.com/cart.php?customfield[1]=someinfo - I need the value customfield[1] to end up on my register.php for a client custom field i've created. It does not seem to work but is there a way to make this possible? Or are there alternatives?

 

I could have the visitor register before purchasing but as a customer myself i would like to evaluate what's available before I register and pay for it.

 

Thank you in advance.