Mark,
As a short term measure for the reccession the goverment have allowed tax bills to be paid by insalments through the following year; ie what was due at 31st Jan 2010 you can pay now in insalments and finishing at next Jan.
BUT this is only for the reccession, so you'll also need to still put some thing aside for what will be due next Jan, so dont get to used to paying that way.
(I believe this scheme is still going, call them)
As someone above, what I do is pay monthly amount by standing order into an account I dont touch when the tax bill comes you have it.
Really we should all also have a contingencing (sp) for repair/replace of equipment/vans, which can happen any time.
Craig