Help in returning html source to field

Howdy all,
I can’t find anyway to do the following, any help would be greatly appreciated:

Here is the scenario.
I have three fields.
I want to take field one(item number) and field two(quantity) and call a javascript script that passes these two fields to a server-side CGI script and have the result be placed in field three(price). The trick is that I don’t want to refresh the page.

I would like something like window.location.href, but return the information back to the same page.

Thanks in advance,
RPGDude

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