Howard,
I picked up your message whilst scanning through today's digests and the current heaving morass of exchanges about Masis (and variants)...
Norris (from one of my favourite UK towns - Settle, see below) gives some sound advice which I fully endorse - but with a couple of small caveats...
In the UK at least, until relatively recently it was the norm for people taking up the discipline to covert old road bikes / frames to use for winter mudplugging - and if they ended up having any talent for it to then progress to paying for specialist equipment.
I've been riding 'Cross on and off for the best part of 30 years and in fact it was only 6 years ago that I coughed for a 'proper' bike (with cantis and big clearances).
In fact my best ever ride in the Three Peaks (see Settle above!) was back in the late 70s when I finished in the top 30 using a 'off the shelf' Dawes with 531 butted main tubes / plain gauge forks and stays and Weinmann c/pulls.
I was not alone in this - take a look at the CR listing for Carlton - and there you'll find a pic of one our greatest ever 'Cross riders, super multi-National Champion John Atkins (unbeatable through the entire 1970s), riding what looks like a pretty bog-standard Carlton road bike with good ole' Weinmann c/pulls...
Probably more than any other branch of cycling the old adage of "it's the rider - not the bike" applies.
Just try and use a light a frame as possible, preferably big clearances all round - so a tourer in 531 d/b with c/pulls would be good - and generally 1 - 2 cms smaller than your usual frame size - extra testicle clearance if things go wrong you know...
I'd also advise not wasting too much cash on specialist knobblies to start with. Here in the UK we have a bike chain called Halfords who stock an own-brand 700c 35 tyre for £10 ($18?) which is supposedly for hybrids - but that has such a chunky tread that I've used nothing else for 'Cross for the last 4 years. The same tyre was until quite recently stocked by Paul Milnes Cycles in Bradford (definitlely a specialist dealer) as the '3 Peaks Rubber' or similar...
I have found that in fact the most limiting factor of most standard road frames is the clearance between the chainstays as they go into the bottom bracket - which can be quite tight even on many 'relaxed' touring bikes - a real mud trap.
Anyway - best of luck - and perhaps let us know how you get on?
Regards to you and all on the list.
Ian Briggs - LUTON UK