Well, since no one else has answered this, I'll take a stab at it.
Let me say from the get go that I've never taken Rituxan for RA. I was, however, treated with it for Lymphoma 5 yrs ago. There may be some differences, but hopefully this will give you some idea of what to expect.
The infusion is given through an IV. My doctor gave me a dose of benedryl when I started, to avoid an allergic reaction. You nurse should monitor you carefully, to watch for any type of reaction. When I took it, I had to have the infusion very slowly, so I took about 5 hours. (Hopefully that's changed)
Afterwards, I had an immune response that felt similar to coming down with the flu- I was tired, achy, had a low level fever, and basically spent the rest of the day in bed. Now that I've got RA, that sounds pretty familiar. By the next morning, I was on my feet, but only moving at half-speed, and the day after that, I'd be fine.
I hope this helps you a little bit and good luck with your treatment!