Form in wap.. help please?

I think this is a basic one (but i aint got a clue about wap coding :S )..

Basically, i run www.nick-web.co.uk , where users can download free colour phone images.. The only complaint iv been getitng is that they think the webaddress is too long to remeber.. so i came up with an idea..

I want to design a wap page, with a bit of text (Thanks for coming to the dowload section, please enter in your 4 digit code below), then have a box for a 4digit code, and then a submit button. When they click submit, whatever the value of the text box was, it would add it to the end of http://www.nick-web.co.uk/wap/ and then after it add .jpg .. so, if some 1 typed in 4334, it would forward them to http://www.nick-web.co.uk/wap/4334.jpg

Any 1 any ideas on how i could do this? I think its less than bout 10 lines of code all in (but i might b worng. lmao).. cause its only the one page..

Thanks .
Nick

*edit* forgot to mention, when they click submit, it will take them to that page.. i.e http://www.nick-web.co.uk/wap/4334.jpg so it downloads automatically.

Thanks, Nick