<form id="form_paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
  <input type="hidden" name="cmd" value="_donations">
  <input type="hidden" name="business" value="paypal@email.com">
  <input type="hidden" name="item_name" value="My Donations Subject">
  <input type="hidden" name="no_shipping" value="0">
  <input type="hidden" name="no_note" value="1">
  <input type="hidden" name="currency_code" value="USD">
  <input type="hidden" name="tax" value="0">
  <input type="hidden" name="bn" value="PP-DonationsBF">
  <label for="">Amount (US$) : </label><input type="text" name="amount" id="input_amount" width="10" class="text" />
  <input type="submit" name="submit" value="Donate" class="submit" />
</form>

<input type="submit" name="submit" value="Donate" class="submit" />&nbsp;&nbsp;
<span id="msg_moreamount" class="icon_warning red" style="display:none;">PayPal takes $0.35 commission for a $1 donation. Please enter at least $1.35 , thank you!</span>
<span id="msg_noamount" class="icon_warning red" style="display:none;">Please enter the amount you wish to donate and try again.</span>
<span id="msg_activity" style="display:none;"> <img src="images/loader.gif" align="absmiddle" />&nbsp;Transferring to PayPal, please wait...</span>

jQuery(document).ready(function()
{
	// the minimum required value to be entered.
	// in this case PayPal takes $0.35 from a $1
	// donation, hence we ask for at least $1.35
	var minimum_value = 1.35;
 
	// attach this script to the form's submit action
	jQuery('#form_paypal').submit(function()
	{
		// check if there is an amount entered
		if (jQuery('#input_amount').val() > null)
		{
			// is the amount equal to or higher than the minimum_value?
			if (jQuery('#input_amount').val() < minimum_value)
			{
				// need more amount
				// hide messages, show more amount error
				jQuery('#msg_noamount').hide();
				jQuery('#msg_moreamount').fadeIn();
				return false; // prevent the form from submitting
			}
			else
			{
				// amount is more than minimum_value
				// hide messages, show activity
				jQuery('#msg_moreamount').hide();
				jQuery('#msg_noamount').hide();
				jQuery('#msg_activity').fadeIn();
				return true; // submit the form
			}
		}
		else
		{
			// no amount entered at all
			// hide messages, show no amount error
			jQuery('#msg_moreamount').hide();
			jQuery('#msg_noamount').fadeIn();
			return false; // prevent the form from submitting
		}
	});
});

.red {color:#ff0000;}
.icon_warning {background:transparent url(../images/exclamation.png) left no-repeat;padding:4px;padding-left:20px;}
form#form_paypal input {padding:3px;border:1px solid #ddd;background:#fefefe;}
form#form_paypal input#input_amount {width:50px;}
form#form_paypal .submit {cursor:pointer;border-style:outset;}

<?php
/*
Template Name: Donate
*/
?>

<?php
/*
Template Name: Donate
*/
?>
<?php get_header(); ?>
<div id="content" class="narrowcolumn">
  <?php if (have_posts()) : while (have_posts()) : the_post(); ?>
  <div class="post" id="post-<?php the_ID(); ?>">
    <h2>Make A Donation</h2>
    <p>If you think you have benefited or I have helped you in some way, by using any of my 
    WordPress plugins or themes, please consider making a donation. Donations support the 
    continued development of my websites and help cover the hosting costs. 
    Donations of any size are gratefully accepted. Thank you!</p>
    <form id="ppDonate" action="https://www.paypal.com/cgi-bin/webscr" method="post">
      <input type="hidden" name="cmd" value="_donations">
      <input type="hidden" name="business" value="paypal@email.com">
      <input type="hidden" name="item_name" value="My Donations Subject">
      <input type="hidden" name="no_shipping" value="0">
      <input type="hidden" name="no_note" value="1">
      <input type="hidden" name="currency_code" value="USD">
      <input type="hidden" name="tax" value="0">
      <input type="hidden" name="bn" value="PP-DonationsBF">
      <label for="">Amount (US$) : </label>
      <input type="text" name="amount" id="ppAmount" width="10" class="text" />
      <input type="submit" name="submit" value="Donate" class="submit" />
      <span id="moreAmount" class="warningIcon red" style="display:none;">PayPal takes $0.35 commission for $1 donation. 
      Please enter at least $1.35 , thank you!</span>
      <span id="noAmount" class="warningIcon red" style="display:none;">Please enter an amount to donate and try again.</span>
      <span id="ppGo" style="display:none;">
      <img src="&lt;?php bloginfo('template_url'); ?&gt;/images/loader.gif" align="absmiddle" />Transferring to PayPal, please wait...</span>
    </form>
    <p><small>Info : once you click on 'Donate', you will be transferred to PayPal where you can enter your payment information.</small></p>
  </div>
  <?php endwhile; endif; ?>
  <?php edit_post_link('Edit this entry.', '<p>', '</p>'); ?>
</div>
<?php get_sidebar(); ?>
<?php get_footer(); ?>