How do you delete an unwanted preset in Lightroom 3 that you have in your saved presets?
FYI, this article from Adobe documents the file location of these presets:
Installed and custom presets and templates have filenames ending in .lrtemplate and are located in folders under the Users/[user name]/AppData/Roaming/Adobe/Lightroom folder.
Another link (for LR4, but I presume this also holds true for LR3) confirms that "factory" or built-in presets cannot be deleted.
I think you can find all your presets in "C:\Program Files\Adobe\Lightroom\Develop Presets" and then delete which are not required. You will find two directories here as "Lightroom Presets" and "User Presets".