Changing Submit Button On A Form To Custom Image?

I'm adding a Microsoft Dynamics CRM Online form to a webpage. It looks like pretty standard html and Javascript. The Microsoft website creates the code automatically and it provides the html code snippet. I provides a standard dull grey button. I'm simply trying to change the standard grey button to a nice looking orange image.

I have the form looking great...only problem is that it doesn't work. I tried it with the standard button and it works fine. When I try to substitute the image, CRM doesn't get the submitted form information. Here is the applicable part of the code:

<input type="hidden" id="dl_qs" name="dl_qs" />
<input type="hidden" id="dl_r" name="dl_r" />
<input type="submit" onclick="document.getElementById('dl_leadForm').dl_qs.value =

[code]....

I tried this, but it didn't work:

<input type="image" src="images/contact-us-button.gif" value="Submit" border="0" <onclick="document.getElementById('dl_leadForm').dl_qs.value = window.location.search;document.getElementById('dl_leadForm').dl_r.value = document.referrer;" value="Submit" >
</form>

I would like to keep any validation built into the form. I'm very new to Javascript, so it's probably something obvious to pros.