Taking a spin of what you asked I'd say you have plenty of choices but it depends what effort and time you have.

If you are happy to sit down and create a fully automated, self-maintaining build (process) then Microsoft has 3 options

MDT standalone FREE
Server + WDS Server licence
SCCM + MDT + WDS Service license + SCCM licence

MDT is the way to create images. Even if you use SCCM, start with MDT. It is quicker, more powerful and is designed for just that. It will fully automate a fresh image creation for you. There is some work with importing drivers but you only need to do it once per machine. It will automate pulling updates down too.

WDS is OK, but I don't see the point of spending money on a server license just to get WDS service, when MDT is free and installs on XP, 7 etc. It's only 25MB but as a later poster says - it gets addictive once you realise what it can do.

SCCM is the ultimate solution but costs an arm and a leg. Being a school I expect that's not practical.

Plan B - if you're happy to just create your source image manually and then clone it, then Ghost, Clonezilla or Acronis TrueImage all work fine. The downside of cloning is what I call staleness. You create your image with Office, Acrobat and Flash, ghost it and sit back. Two weeks later Adobe release a critical update for Flash. You have to create your gold image all over again, or somehow get Flash out to every netbook. with MDT it would take about 10 minutes, not including the download!!

SCCM gets over that pain by having full software distribution

Summary: Get MDT install it and experiment. It's easy and really effective. If you get stuck I'd recommened Deployment Fundamentals by Johan Ardwidmark. It's only £8 for the Kindle version which is a steal .