On the phone tick "Unknown Sources" in Settings > Applications.
Download, extract and install the Setup .exe.
Setup.installAPK.zip 683.9K 2770 downloadsDownload, extract and install the usbdrivers if you don't already have ADB set up.
usbdriver.zip 3.14MB 1958 downloads(NB: ADB isn't necessary to use InstallAPK)
Once installed, .apk files should show an Android file icon.
Double click an .apk to install to a connected phone.
Credit to Paul from Android @ MoDaCo for this