Windows Movie Maker.

Hi All,
I am new this so any advice you may give, please give it to me in simple terms... I am not very computer smart!
O.K I have spent days working on a movie through movie maker. I had the one that comes pre-loaded on Acer Aspire 6920, running an operating system of Vista. When it came to burning it shows there are no DVD burners in drop down list of Windows Movie Maker. So I went out and bought an external DVD maker and still have the same problems. Thanks to forums on Google, I found one site that said I should change the Jmicron JMB36X flash media contoller and that I would be directed to re-start. Well it never changed this media controller - it deleted it! It is nowhere to be found (that I can find; on my system - don't I need a media controller to make this program work?
So I had a brain wave today - why don't I just install an upgrade of windows movie maker. Found (what I thought was the appropriate upgradge for movie maker... it installed and when I go to look at the movie I saved, it has red x's throughout - ie not playing movies & photos I had added to the timeline... arrrrrhhhhh!
So I need your assitance in getting this up and going again so I can finally burn this movie... it really has become a bain of contention in my life at the moment - please, please, please help!?
System info:
Windows Vista home premium
Service pack 2
Acer Aspire 6920
Rating Index: 3
Intel(R) Core(TM)2 Duo CPU
T575 @ 2.00GHz 2.00GHz
Ram: 2GB
System type: 32-bit Operating System
If yo need any further information to provide accurate advice, please give me instructions on where I can locate the information and I will do my best to get it to you.
Cheers
Rachael