(Disclaimer: You can do this using Foobar2000 or dbPoweramp easily enough. For those of you who don't use those apps or can't be bothered, read on...)
NOTE: This method does not work for file names with Unicode characters in them (use Foobar if you want to convert those types of files). Also, this will only add id3v1 tags to the mp3 files - you may want to add in id3v2 tags in with a program such as Mp3tag or MediaMonkey.
OK. Here's a little tutorial for those of you who would like to convert Flac to mp3 using a simple little freeware app.
First, if you don't have them yet, download & install the Flac (FLAC for Windows with installer) and Lame mp3 codecs. Next, download & install this small & simple app called All2Lame.
*You may also need Tag (by Case), which is used for adding ID3 tags to files. It can be found on the All2Lame homepage.
http://flac.sourceforge.net/download.html
http://www.free-codecs.com/Lame_Encoder_download.htm
http://members.home.nl/w.speek/all2lame.htm
Now that you've done all that, open up the program. You'll need to point it to the codecs that you just downloaded. Do this by clicking on "Locations" and then browsing to each one.
http://i151.photobucket.com/albums/s136/WoodenhHead/all2lame1.jpg
Next, you'll want to add a command line (or a bunch or 'em) to the "Switches" box at the bottom. These command lines tell the program what bit rate to encode at. Click the " " button beside it to add new ones. Later on you can just click the arrow button there to bring up whatever command line you choose, for different bitrate encodings. Here's the ones I use:
-b 320
-V 0 --vbr-new
-V 2 --vbr-new
You will want the "Add ID3 tags" box checked, and you can configure that option how you want. (I just use "Copy tags from source files")
Now you just add the files you want converted, choose a command line, set the "Output folder" location, and then click "Encode". A DOS window will appear, showing the process in action. It doesn't take too long.
http://i151.photobucket.com/albums/s136/WoodenhHead/all2lame2.jpg
That's it! After that initial setup, it's a very quick & simple job whenever you want to encode Flac to mp3. Also, if you like, you can click "Decode" to decode to .wav files.
Cheers!