hi. do i need to buy a graphics tablet to do good vector art?

I can say: no ! (my own opinion)
I have a cheap one but i use it only for some work in gimp. All my graphics made by using the standard PC mouse.

No, you dont need one, but you may find it makes life easier.

Not at all, but it's nice to have. One of the great things about vector art is that you can tweak it so easily using nodes, so it's not hard to use a mouse. Having said that, I have a Wacom Intous 3, which is a pretty good tablet and I love using Inkscape with it. Using the calligraphy tool is obviously much easier.

For art in the GIMP I'd say it's pretty much essential!

I don't use my Wacom that often in Inkscape but I'm glad that I have one in my toolbox. There are certain free hand motions that are difficult to do with a mouse. For instance, take your signature. It's easier to write that with a pen instead of a mouse. If Inkscape had some sort of air-brush tool then I would probably use my Wacom even more.

There's nothing you can create with a tablet that you can't create without one.

In fact, for those who believe you need it for raster work, some of my favourite artists do the most amazing painting with just a mouse. I don't know how they do it

to tell you the truth the only real difference between how well a tablet works compared to a mouse is personal preference ive been working in graphic design for about 4 years and the first 2 years i started i didnt even think twice about a tablet, and when i finally got a tablet the thing i noticed was not the quality of my work improving but the production time was almost cut in half because you no longer have to manually place points and play with them to create a curve you can flick your wrist and create an almost perfect curve, the key word is almost though because no matter how smooth your hand is you will always have a couple of points to correct but you wont have to correct them all.