LaTeX is a typesetting system used on many mathematics and computer science journals.
Compared to the typical word processing document, you'll get an highly professional looking document without having to waste your time on fiddling with the looks of your document.
For some reason, the Open University requires you to submit all of your work in Microsoft's 'Word 97/2000/XP' ('.doc') format.
It is possible to convert LaTeX documents to that format, although the result does not look very pretty and there are there are some problems with including pictures. I've had reasonable success with the Debian package mk4ht and the following command:
mk4ht oolatex some_tma.tex some_tma.odt
The resulting document is in the ODT format (used by OpenOffice et. al.) and you can use OpenOffice to convert it to .doc.
I suggest you use pdflatex to always submit a PDF file together with your .doc and insert a respective note into your document.