I don't know of a guide, but I can help a bit.
Start up AVStoDVD and click on Preferences at the top of the screen. This gets you into the part of the program where you can set up paths, and encoding settings. You'll see a window with a few tabs.
In the System tab, put a check mark in the box to enable multithread encoding if available.
Click on Paths and set up the places on your hard drive where you want the output and the working files.
Next, on to the AviSynth tab, where you might want to put a check mark in the PAL speedup for NTSC film to PAL box (since you are in England, and use PAL standard for dvds).
In the Video tab set the dvd video standard to PAL. Also put a check mark in the box to keep dvd compliant video.
In the Audio tab, audio should be AC3, and bitrate should be 224 for most encodes. Put a check mark to keep compliant audio. AC3 encoder should be Wavi + Aften unless you run into some problems with that setting.
Once you are done, put a check mark in the box to save current preferences as default, then click OK.
Now lets take a look at some of the other controls on the main page of AVStoDVD. You'll see a control for DVD Size, either DVD-5 single layer or DVD-9 double layer are the normal sizes, though you can make a custom size too.
Output allows you to change what type of video is produced. Most of the time you will want dvd video folders.
DVD Menu lets you get into the dvd menu wizard, so you can make menus for your video. This can be handy if you want to make a dvd using several different videos as input. You can access each video separately this way.
To import an avi file to the program click on the green + sign on the right. This lets you search your computer for the file and insert it into your compilation.
If you want to examine what the encoding parameters are for the video, click the little gear icon just under the green + sign on the right. This lets you see which encoder the program has selected to work with your input. I very much prefer HCenc over the Quenc encoder that is also included, so I normally change it if Quenc has been selected. To do that, unclick Auto Video Setup, and change the encoder to HCenc VBR 2-pass.
Now lets say you have a foreign film and wish to add subtitles. Look at the video you've added in AVStoDVD. It should show the video and audio streams. Right click on the main window of AVStoDVD, then click on Subtitles. This lets you navigate to the place on your hard drive where you have the subtitle file and adds it to the dvd-video you are making.
You can adjust the type of menu for the dvd if you wish. To do so, click on DVD Menu and run the Editor. Once done with changes, just close it and the changes will be applied.
If you are ready to start the encoding, click on the big Start icon at the bottom right of the main window.