Hi @quittoo, the steps in the post that pertain to aweber integration: http://forum.webflow.com/t/aweber-form-integration/8207/4, are pretty much the same as the integration for this form integration.
Where the post talks about the aweber mail script, you substitute that with the form url you are posting to:
http://exitus.theultimatesystem.com/ms/external
In step 2, you copy the hidden fields from the code they provided you into an embed widget placed inside your form, just above your submit button:
<input type="hidden" name="event" value="lp_form">
<input type="hidden" name="sub_event" value="visit1">
<input type="hidden" name="revisit_event" value="revisit1">
<input type="hidden" name="val_required" value="f_firstname,f_email">
<input type="hidden" name="category_id" value="66394">
<input type="hidden" name="campaign_id" value="9024">
The fields in the code they sent you are named liked f_firstname, f_lastname etc, so give your Webflow form input fields, the same names as used in the code.
I hope this helps. If not, please let me know – I’m happy to assist further! 
Cheers, Dave