There's a newer release available.
Last Sunday I decided to build a foursquare sidebar widget for BlogEngine.NET since there wasn't anything around yet. The current version simply shows the last places you've checked-in and is mostly based on the twitter widget from Mads Kristensen.
In order to use the widget you will need to have .NET 3.5 installed on your server. I will probably port everything to .NET 2.0 later, but since I was used to work with LINQ, I implemented everything in .NET 3.5.
First of all download the current version available at codeplex. Extract it and upload everything to your BlogEngine directory into the widgets folder. If you've uploaded the files and switched your current BlogEngine installation to .NET 3.5 you're ready to open your site in the browser and add the widget to the sidebar.
After you've added the widget, you'll have to specify some settings regarding your foursquare feeds. Simply open http://feeds.foursquare.com and copy-paste the urls for the rss and kml feeds into the according input fields inside the foursquare widget edit section. Then go to your foursquare page by clicking on me in the navigation bar at the top, copy and paste the url into the account url input field. Next decide how much your feed should be requested from foursquare. But keep in mind, that if you choose the number of request per hour to high you might get blocked by foursquare. I guess every 15 minutes should already be enough for the average user. Finally choose how many check-ins you want to display on your blog. Next save your settings, and then you're ready to enjoy foursquare together with BlogEngine.NET.
It's possible that the BlogEngine application has to be restarted, after you have added the foursquare widget.