I've never seen anyone jump to a 5D to begin with. No matter which one you buy, you'll need a lens that can work well with landscape. The 17-40 lens for Canon would be your best bet with the 5D. You'll have to get used to the depth of field compared to a point and shoot. Point and shoots usually do better for new people to photography, with landscapes, due to the smaller sensors which will increase the depth of field. This way it makes it easier to have everything in focus.
If you have that type of money then you could look at the Nikon D700 that just came out or Canon should have a replacement for the 5D shortly, since it's a three year old camera.
Actually if landscape is going to be the main subject then the Sigma DP1. Here are some links that might help you on this one.
some sample landscape photos
This article compares it to the 5D and E-420
I'm debating on which camera to upgrade to for large landscape prints, and I'm new to SLRs in general. I'm between the Pentax K20D, Nikon D300 and the Canon EOS 5d. I'm leaning towards the EOS 5D mainly because of the large sensor size and it looks like the cheapest full frame SLR. Any other suggestions for cameras that would be well suited for large landscape prints?
I'm also completely ignorant about lenses, and I am thinking of buying from EBAY because I see a lot of packages which include around 5 lenses for a pretty good deal. Let me know if I'm wrong about that.