Accessing value of textbox

Probably a simple fix, but it's driving me nuts.

I have a form for users to fill out. Submit button at the end. But halfway through the form I have a link that carries the user to a different page to flag some database entries to include with the original form. I have worked out the passing to the flagging page and getting back except for filling in the data they have previously filled in before taking the detour.

What I would like to do is store the value of the textboxes, pass them to the new page, then have that page process itself. At the end of that processing it redirects back to the original page and fills in the text boxes previously filled in.

I hope that makes sense. Thank you.