It's easy. It took about an hour,
Follow the instructions - there's a PDF guide that was easier for me to follow. Unless you have multiple wmc installations, you will be doing the client and server on the same machine (the server fetches the guide data, the cline imports it into wmc).
You are doing a clean install of epg123, not windows. So just follow the instructions. Click step 1 which will clean up wmc and start fresh. It also makes a backup of your wmc configuration. Step 2 will take place in wmc and EPG will launch wmc automatically. The setup will be right beside it. You click that, then click "I do not agree" on the setup. This will download setup data, but by not agreeing it will reject it. This is ok. Go through with the rest of setup. When it comes to detecting channels, leave it - it must detect all 10,000 channels (this was not clear in the docs).
Don't worry,this will all fix itself in short order. After setup is done, close wmc, it's been prepped for epg123. The rest of the configuration is in the server app for now where you log into schedules direct, get the right lineup, and download the data. The data will be processed and all that. At this point, it will then ask about your season passes - it will try to line up as many as it can automatically. The ones that say "manual" are manual recordings and can't be fixed up. But the ones that are automatic can. Epg123 will try to line up the ones it can but there will be a few it can't. You highlight the few it can't, and manually search for it. If it's a show that's cancelled, you can't recreate the season pass. It works fairly well - the ones it can't fix up usually are shows that have similar titles or are named slightly differently. The poor quality of rovi data is partially the cause - show names get misspelled or abbreviated wrongly so an exact title match that epg123 uses will fail. The manual match lets you find the right show.
And after that you let it process and go. The client app will start up and you'll see the list of channels and the list of schedule channels, and they will be matched up. I use match by channel numbers as I'm on cable and it corrects for the changes in station names.
It's a simple process,really. Epg123 has been around for years and the setup process has been simplified greatly and it's quite painless.
If you're really unsure, make a system backup before you start so you can easily revert. And pick a day when you have fewer recordings and at least a couple of hours before a recording is to start, so you have plenty of time to set it up before potentially losing the recording,
It's easy. And there's lots of documentation.