You will have a great trip! Oxford is a great place to visit - but pretty bad to drive around. I lived there for 4 years and had a CB750F2 while there. Getting out of Oxford though and the Cotswolds beckon with their narrow stone-walled roads, quaint thatch-covered English villages, and hilly, twisty terrain is a must on a bike! I had some great times there. Dont miss the White Horse south of Abingdon -nice ride and also there is a great roadside biker cafe hangout (a real one!) on the road between Oxford and Reading where on weekends you can get your ham sandwhich, coffee and hang out with 100+ other bikes who have dropped in to warm up. In fact riding anywhere around Oxford is good!!!
Dont miss The Trout pub -on the edge of Oxford - its an old stone pub by the river with a picture-esque stone bridge over the river and some good walking on the other side of the pub. There is a Honda dealer in Oxford (a few dealers in fact) - google them and write asking about rentals. That would be your best bet.
Dont miss the ride out to Woodstock and Blenheim palace - both at the edge of the best riding - the Cotswolds ;-). Further afield you can head for South Wales and have even more fun there.
Weather in March is variable - can be cool (36 -45F) -bright, sunny to rainy. Oxford is usually fairly dry though.
Oxford sites not to miss - Christchurch college - walk down to the river from here and back up to Magdalen College/botanical gardens....from here walk along the back alleyway to the Bridge of Signs and you`ll be in front of the Matriculation Hall...take a left and you`ll see Radcliffe camera and the Reading room of the Bodlien library which is on your right...also here is Brasenose College and All Souls college.
Note -at the Bride of Sighs you will see a tiny alleyway...go down here and you will find The Turf pub...great place for a beer...watch out for low ceilings ;-).
London - riding here is also good fun but you`ll need to be careful of everyone else - its legal to split lanes and everyone does it. Watch out on roundabouts.
Anything specific let me know.
** if you want to meet some original "cafe racers" go and see Dave Clark at
http://www.daveclarkemotorcycles.co.uk/. Check out the gallery on the website....Old school backstreet place. The father who still works there knows everything about bikes - real character. He may remember the tall Scottish guy with the 1974 orange Honda CB750 - he took a hammer to my steering-head bearings - this was back in 2003/2003.
cheers
Andy