Default behavior
By default, if you type in an incomplete URL into the IE Address bar in IE 5.x or later, Internet Explorer will automatically try to find the URL you want. For instance, if you type in simply "company" rather than "http://www.company.com" IE will try company.com, company.org and company.edu (IE 6 will additionally try company.net). If there is a match, IE will display that URL.
You can expand this list
Add the following Registry entry:
Hive: HKEY_LOCAL_MACHINE
Key: Software\Microsoft\Internet Explorer\Main\Url Template
Name: n
Data Type: REG_SZ
Value: www.%s.domain
Replace n with a number (IE will autoscan in order, starting with 1,2, etc.) Replace the word .domain with the actual domain you want to search (for instance ..gov, or .UK. Remember to use caution and frequent backups when editing the Registry.