Tours of Giverny

I don't know anything about tours to the gardens, but I will say that doing it yourself by train from St Lazare to Vernon then a nice walk or easy bus to the garden are realy easy, then the garden and house are very self explanatory. Especially if you are familiar with the works of the artist and can recognise viewpoints.

If you are on a tour you have to go at their speed and look at what they want you to look at.

It really is very very easy to do it on your own.

I did what Nigel suggested. Train from Gare St. Lazare to Vernon. There is a bus to Giverny right outside the train station. When the bus arrived in Giverny I took a picture of the sign that showed the times for the bus to return to Vernon. I think there may be a Fat Tire Bike Tour of Giverny.

I've always done the train/bus combo to Giverny, and then on to Rouen by taking a train at about 1:00, spending the afternoon and then heading back to Paris for dinner. But I think you could also amuse yourself for a couple more hours in Vernon and environs before heading back to Paris.

Get there early, or go in the off-season. It turns into a conga line around the pond after the tour buses arrive.

--Dav

Dav is right, take an early train from Paris so you get to Giverny when it opens. I did that and was one of the first ones into the garden and after I was done in the garden I went into the house and by then the gardens were getting very crowded. It's easy enough to take the train to Vernon and get the bus to Giverny which waits at the train.

Don't visit after lunch during peak summer months, the line is right down the road. We arrived as soon as it opened and it wasn't crowded at all. The restaurant opposite was fantastic, we sat outside and I have the most amazing Monet's Salad.
You don't need a guide to take you round, the garden was much smaller than I imagined and we were done in around an hour.