I actually found a trick that works with igoogle and it's here:

http://www.google.com/support/forum/p/Web+Search/thread?tid=5a69f1094357f31b&hl=en&start=665

Open your "hosts" file in a text editor.
Add the following:
127.0.0.1 clients1.google.com
127.0.0.1 clients1.google.co.uk
(or use whatever else .tld Google uses in your locale)

Thank you misexistentialist, I tried your suggestion and it works with regular search, however not within iGoogle. There is a relevant discussion here as well as some suggested workarounds.
http://www.google.com/support/forum/p/Web+Search/thread?tid=5a69f1094357f31b&hl=en&fid=5a69f1094357f31b000491ad247e1433&hltp=2

I'd like to have the option to turn autocomplete off. I've found that it often leeds to suggestions that are inappropriate for children.