Generating A Post Request For PayPal Button In C# ASP.net?

I'm trying to allow a web form to use a PayPal buy it now. The relevant page is: [URL]

Based on which radio button a user selects, depends on which paypal button they are "redirected" to.
The subscriptions are easy - they are just a simple redirect.

The last option, requires a user select a venue. For this, i require to use the form below:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="10956105">
<table>
<tr><td><input type="hidden" name="on0" value="Venue">Venue</td></tr><tr><td>
<input type="text" name="os0" maxlength="60"></td></tr>
</table>
<input type="image" src="https://www.paypal.com/en_US/GB/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online.">
<img alt="" border="0" src="https://www.paypal.com/en_GB/i/scr/pixel.gif" width="1" height="1">
</form>

But of course, I want to do it without using that form.

What I have so far is:

if (singleOneOff.Checked)
{
paypalForm.Text = getPaypalForm(venueSelect.SelectedItem.Text);
var strJS = getPayPalPostJS("_xclick");
paypalJs.Text = strJS;
var xxx = "dd";
}

This determines if that particular radio button was ticked.

getPaypalForm
private String getPaypalForm(string venue)
{
StringBuilder strForm = new StringBuilder();
strForm.Append(@"<form action=""https://www.paypal.com/cgi-bin/webscr"" name=""_xclick""

[Code]....

However, if i select the radio button, and a venue, and press the button, nothing happens....

I followed this guide: [URL]