a spinal tap is used to diagnose MS alright. I had one done (two actually, the first one didn't yield enough spinal fluid to be useful) and it's standard practice after an MRI. It doesn't help you exactly - it just shows up whether you have oligoclonal bands in your spinal fluid, which is a sign of MS.
Tami I hope you're feeling better soon - the whole testing and diagnosis is a very stressful time for anyone.
RR-MS dx 1998 and Coeliac dx 2003
Copaxone, Cymbalta. EPO, Fish Oils, Vitamin D3 2000 IU daily, Cal/Mag/Zinc, Multivitamin/mineral, Co-Enzyme Q10, Probiotics, Milk Thistle.