How to change checkout_success URL

Hi

Zen cart sits in an iframe within a complete website and works really well. The trouble is that after the checkout, customer is redirected back to http://www.fizzyparts.co.uk/parts/index.php?main_page=checkout_process
instead of http://fizzyparts.co.uk/success.html?main_page=checkout_process which is where I told PayPal to send customers after a successful payment.

Typing the url in a browser does take me to the correct page, but it seems the instructions I'm giving Paypal are being overridden.

Is there a file/variable that I can edit to ake sure the checkout_success does indeed return them to the site (with the relevant page showing)?

To see site: http://fizzyparts.co.uk

TIA

that wont work, the file in question is actually in the shop folder,
and needs to run from there,

the downfalls to running in a frame,
If you search I believe this has been discussed in detail before

I'm still searching :(

I tried to chage it to just the .../sccess.html and while it works locally, it seems that PayPal gets overrideen by the IPN module; my problem is I can't seem to locate which variable I need to change in which file....

Cheers

More than one thread on the same subject gets very confusing. Please continue in the PayPal Thread.