I work for a very large University, we use a combination of use Norton Ghost, and a number of other tools to manage our SOE (Standard Operating Environment). We also use SysPrep before we image the machines before we make an image.
Make sure that you install all of the drivers for each of the different PC types on the image you are rolling out. To do this Audit all of the computers to see what hardware they have got and group them into similar hardware type (usually by motherboard chipset type). Make an image with Ghost of the biggest group, then install that image onto one of the PCs from the next group of PCs, and update the drivers. Do this until you have copied the image to each different hardware type and the final image will contain the drivers for every different hardware type. When some new computers (with new hardware) come in, we install our image onto that PC and update the drivers.
For the longer term it's best to convince procurement of the advantages of buying exactly the same type/brand/model of computer hardware for this to work smoothly.
It would be easiest for you to make a Ghost image on a bootable Dual Layer DVD (We use the BartPE environment, but there are many simple bootable CD/DVD solutions
With a bit of planning an a little bit of hard work you can make it very easy to manage a very large number of computers with a very small number of people (we have 3000+ PCs and Laptops, 400+ Blackberries, 500+ iPhones, 750+ Printers and there are 8 techs; we still have time for drinks on Friday afternoon!)