OnChange Lookup ASP Recordset

I have a form on a webpage that someone enters a number (SponsorID).
After then enter that SponsorID into the form, I need to somehow query
my SQL database and find the record that has the same ID as the
SponsorID entered into the form and return the SponsorName (and write
it out on the page using a <div> tag or something of the like) WITHOUT
reloading the entire page (because I will loose the other information
already input on this page).

Now, I don't necessarly have to query the database, I *could* create
an Array when the page loads, using ASP, that will contain the
SponsorIDs and the SponsorNames and then compare the SponsorIDs within
that array with the number that was entered on the form.