Funny you should ask. I just did this a couple of weeks ago for a family project.

Go to http://www.chienworks.com/media/flamingtext/ to download a .veg file and three images. I used stills for the demonstration to save space, but you can use video clips instead.

The top track contains the generated text, white with transparent background. It is linked as a parent track to the fire in the second track, which is a child. The third track contains the video that the flaming text is superimposed upon. To join tracks 1 & 2 as parent/child, click on the crooked arrow icon at the left edge of the track header for track 2.

To add to what's been said,
The use of takes is the icing on the cake here. Everything you do on your text page/key matte can carry over in a clip inherit deal to the key fill.
Animate some text via keyframes for kerning/scale/deformation in the Text tool then add some filters at event level. Pan/Crop to hearts delight.
Right click drag that tweeked text event and snap to track below it. Make copy, new source. Right click drag your clip/fire from explorer window (only) and drop it on that copy of text on lower track. Add as a take, video only if needed. Now your fire will follow the text. Turn off, adjust and add filters as needed. Glow at track motion level in orage makes for tasty fire fill fonts. Using the glow filter at event level can let you blow out your graphic in a nice organic transition. Differnt fade rates does some cool stuff with the track motion glow.
Gets a little tricky with tracks working with key filled text. Best to bounce up to new top track for main video work, drop down to key filled tracks as needed. What looks like limits for transitions in and out of keyfilled text really isn't.

Craig H.

Thanks everyone for the help.. I will give this a try and let you know how it turns out.

Ulead Cool 3D can create 3D flaming text as a preset drag and drop.
$50 dollar program. You can bring them into Vegas and lumakey.