Here are some instructions I found that remove it. Didn't try it myself but the instructions look ok. Try the manual method if the other method doesn't work and you feel comfortable with the Registry Editor.
http://www.kephyr.com/spywarescanner/library/incredifind/index.phtml
Overview
IncrediFind is an Internet Explorer browser helper object that changes your Internet Explorer error page to sirsearch.com.
From the developer: IncrediFind is a free utility for Microsoft Internet Explorer version 5 or later that provides contextually-relevant search results in place of unfound and unavailable web pages, and allows users to search the web by simply typing any keywords or search terms in their Internet Explorer address bar.
Uninstall procedure
Uninstall IncrediFind from "Add/Remove Programs" in the Windows® Control Panel.
Manual removal
Please follow the instructions below if you would like to remove IncrediFind manually. Please notice that you must follow the instructions very carefully and delete everything that is mentioned. In most cases the removal will fail if one single item is not deleted. If IncrediFind remains on your system after stepping through the removal instructions, please double-check by stepping through them again.
Start the registry editor. This is done by clicking Start then Run. (The Run dialog will appear.) Type regedit and click OK. (The registry editor will open.)
Delete 'HKEY_LOCAL_MACHINE \ SOFTWARE \ Classes \ CLSID \ {5D60FF48-95BE-4956-B4C6-6BB168A70310}', if it exists.
Delete 'HKEY_LOCAL_MACHINE \ SOFTWARE \ Classes \ CLSID \ {4FC95EDD-4796-4966-9049-29649C80111D}', if it exists.
Delete 'HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows \ CurrentVersion \ Explorer \ Browser Helper Objects \ {5D60FF48-95BE-4956-B4C6-6BB168A70310}', if it exists.
Delete 'HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows \ CurrentVersion \ Explorer \ Browser Helper Objects \ {4FC95EDD-4796-4966-9049-29649C80111D}', if it exists.
Exit the registry editor.
Restart your computer.
Start Windows Explorer and delete:
%ProgramsDir%\IncrediFind\BHO\incfindbho.dll
Note: %ProgramsDir% is a variable (?). By default, this is C:\Program Files.
Start Microsoft Internet Explorer.
In Internet Explorer, click Tools -> Internet Options.
Click the Programs tab -> Reset Web Settings.
