Both sideshowbob and Bottleneck are recommending Moving Coils BUT possible word of warning.  I don't know - maybe some one here can tell me - but just how well is that R200 arm going to cope with an MC?  I would imagine given its vintage, that its likely pretty low mass and better suited for a highish compliance MM - might not do so good with low compliance MC carts.  If it was an RB250 or 300 it'd be a different story, but it isn't.

Dunc.  Fitting a cartrdige isn't too hard.  There's plenty of help to be had online.  Here's an example which covers it pretty well (and includes a usable alignment protractor to print out and use).

http://www.hi-fiworld.co.uk/hfw/featureshtml/cartridgetweaks.html

One thing that'll make it easier for you by the looks of it is that the arm you have has a detachable headshell, which ought to make a fiddly job easier.  Three words of advice

1) Take your time

2) MM carts usually have removable styli MCs don't.  If you go for an MM cart like the Goldring 1006 removing the stylus before fitting the cart remove a lot of the danger and stress.

3) Don't do it drunk or stoned (a mistake I made ... once    )

You really can't go too wrong with the Goldring - and it has the bonus that you can upgrade it by repalcing the stylus - right up to 1042 level (same is true of the Ortofon 5x0 range of carts). 

I could be wrong about MC carts and that arm, but if I'm right the results may be less than pleasing.  There is some discussion of the issue of cartridge compliance (basically the rigidity of the cantilever - the lower the compliance the more rigid) and tonearm mass here http://www.xs4all.nl/~rabruil/ttcartridge.html) - its to do with keeping tonearm/cart resonances out of the audible range.  Generally speaking low mass arms need high compliance carts and vice versa.  MC carts are usually a lot less compliant than MMs.  That old arm of yours is almost certainly of mid 70s vintage and likely a low mass design.  In the 70s received wisdom suggested low mass/high compliance was the way to go - and so higher compliance MM carts may suit it best.  The RB250/300 is sort of mid mass and so will pretty much work with either.  Does anyone know what the effective mass of the old R200 (or the Acos Lustre) is or am I in fact barking at the moon?

PS.  Those "hot and bothered" sibilants.  If its there on all records throughout the record its almost certainly a duff cart.  If its there on all records but gets worse on inner tracks then its more likely misalignment (which if not sorted could damage the records).  If its there on some records but not others then its more likely the records themselves that are damaged or worn.  Really though as I think you've already concluded - if you don't know the provenance of the cart its safer to bin it.