Producing posters using Latex is very possible! The a0poster class lets you produce output in A0 size as well as producing correct font sizes. This should appear in the preamble of the latex file.

\documentclass[a0]{a0poster}

In addition the textpos stylesheet lets you position text in the poster.

\usepackage[absolute]{textpos}

Setting up the grid
The position of the grid in which the text is placed is setup with the command:
\TPGrid[40mm,40mm]{23}{12}
Note that [40mm,40mm] is the margin round the edge of the page.
Here we use a 23 x 12 grid. This gives us, for example, four columns of width 5 boxes, with a gap of width 1 in between them. The same dimension allows, eg, three columns of width 7, with gaps of 1 in between. We have also 12 vertical boxes.

Textblocks
Understanding textblocks is the key to being able to do a poster in LaTeX. In the LaTeX file, text is placed in blocks using the commands:

\begin{textblock}{wid}(x,y) ... \end{textblock}

the first argument gives the block width in units of the grid cells specified above in \TPGrid; the second gives the (x,y) position on the grid, with the y axis pointing down.
Note: You will probably have to view the output (more than) a few times to check that the positioning is ok.

Viewing the poster
You can use the dvips command to produce a postscript file. Alternatively you can use pdflatex to produce pdf output. However if you use pdflatex, then all pictures and graphics must not be .eps. Tiff, jpg, pdf etc is fine however!

Finally, if you are going to get your posters printed by Media serivces in Glasgow Uni, then you will need to produce the poster in tiff format. It's straightforward to do this. Open up Gimp or some other image package, and simply save the file as .tiff. Easy!

Here is a sample LaTeX file, and the corresponding pdf file.

An excellent page with much more information on LaTeX posters can be found here.