Install a APK from the sd card on the phone? Yes, it's possible.
1: Go to Settings>Applications and check Unknown Sources.
2: Install a file manager like Astro (via the market)
3: Open astro and browse for your apk, and click on it to install.
ES File Explorer is good too. it will allow wireless LAN browsing through your home network. just click on the apk in the folder it is in on the PC and it will automatically transfer the apk to the SD card and ask if you want it installed.