Another issue you might face once you manage to get two blogs on one page is how you'll get them to display side-by-side. Probably the easiest way to achieve this is to make a table, but that's so 1998. I use CSS positioning, instead. It's a little harder to set up, but it's worth it. It makes your code much easier to read and maintain. This page you're looking at right now uses CSS to display two columns of text. Feel free to view the source and borrow whatever looks useful to you. All the necessary styles are in the <head>. The #leftpanel and #rightpanel divs hold the columns. The #container div centers the whole thing, using the nifty auto margin trick.
For more on CSS multi-column layouts, check out BlueRobot or glish.
Speaking of viewing source, wouldn't it be nice if you could see a great example of how to include two text files on one page by looking at the source of this page? After all, this page uses PHP to include two text files. Try it. Right click (or do whatever you Mac people do) to View Page Source. Huh? The PHP code is nowhere to be found. That's because by the time the file gets to your browser, my web server has already executed the PHP code, replacing it with the contents of two text files.
This is easily remedied. Here is an exact copy of this page with one small but critical difference: the file extension is ".txt" instead of ".php". Without that "php" extension, the server doesn't execute the PHP code. It displays it. If you want to see what the two included text files look like before the server includes them on my page, click here and here.
If you want to get a two-column PHP page up and running as fast as possible, you could just save the .txt verson of this page, upload it to your PHP-enabled server, and rename it with the .php extension. Then you can put whatever you want, including blogs, in two text files with the appropriate names, and you're off to the races.
If you'd rather set up your two-blog layout with Server Side Includes instead of PHP ('cuz you roll oldstyle), here's an SSI example page.
At the bottom of this page, I've included Amazon links to four books and a piece of software that I use all the time to make my websites better. If you follow one of those links and buy anything, I'll get a little kickback. Nothing says "Thank you" quite like a kickback.