Change part of an HTTP GET request

[andradrr]

Hi everybody!

Please, can anyone help me with a problem.

I would like to change only a part of an HTTP GET request. When I click on a given site to watch a movie the browser sends the following request to the server:

Link clicked:
http://prxbx.com/members/materials/strea...position=0

Header captured by Proxomitron:
+++GET 1031+++
GET /members/materials/stream2.php?file=0017m/medium/0001&position=0 HTTP/1.1
Accept: */*
Accept-Language: pt-BR
Referer: http://prxbx.com/members/loader2.swf?v1.3
x-flash-version: 11,6,602,180
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2; Tablet PC 2.0; WWTClient2; .NET4.0C; .NET4.0E)
Host: hotkinkyjo.xxx
Cookie: PHPSESSID=rqeuleevhsqstfsgjhac61v9a7
Connection: keep-alive

What I would like to know is how do I change the last part of the URL request from "position=0" to anything else like "position=12345"

I just need to change the position number that follows the "=" sign from "0" to another number.

I've tryed to play with "URL:" header command but I could not figure out how to do that.

Thanks a lot in advance for any help.

Cheers.

Edit JJoe: Change site to prxbx.com