Which would be the best camera for a bigginer?

Okay, then. Since it seems like you're generally familiar with digicams and basic photographic terminology, let's go through your options.

There are plenty of ways to step up from the consumer point-and-shoots like the one you've been using. You could go ahead and take the jump up to the dSLRs, or you could take a smaller step up to a "prosumer" camera, one that blends the easy usability of consumer models with the advanced, optional features of SLRs.

(It should be noted that sometimes "prosumer" is used to indicate low-end, reasonably priced dSLRs as well as high-end consumer cameras. In this response I'm going to use it only to indicate high-end non-SLRs.)

In the prosumer category there are literally hundreds of quality viable options. I recommend narrowing your search by determining which features are most important to you. Do you care about huge resolution, or is a more pedestrian 5 or 6MP ok? Do you need a super zoom of 10-12x, or are you ok with a more traditional 3-5x? Do you want something tiny, or is a little bulk ok? On the very low end of the prosumer scale/high end of the consumer scale you've got cameras that generally look like consumer cameras, but sport some extra bells and whistles. Canon's A-series, for example, blends a snug pocket fit with some unusually advanced manual controls. In the genuine prosumer range you have cameras that LOOK more like SLRs and sometimes behave in much the same way. However, they lack several important features as compared to SLRs, mainly customizability of manual controls, the ability to change lenses (though some have adapters for a limited selection of add-on lenses), and pro-quality photographic sensors. Top performers in this range include Sony's F717/828 and H2/H5, Canon's G-series, and S2/S3 IS, Fuji's S-line, Kodak's P-line, Casio's EX-P series, Panasonic's FZ-line, and so on. All of these cameras offer high MP, high zoom, a solid feel in your hand, and great performance to some degree.

The low-end SLR market is similarly crowded, with offerings from Canon, Nikon, Pentax, Olympus, and even Minolta (recently acquired by Sony). Again, all of these cameras offer great features and performance, and to compare all of them at once would be a task beyond anyone's powers. I can only recommend that you go to your local electronics superstore and try their demos out in your own hands. Holding these cameras and shooting them, not to mention paging through their menus and checking out their controls, is the surest way of finding a match for your own wants and needs. This, of course, goes for the prosumer cameras as well.

As to your original question regarding the 400D, no. I don't think it would be too much for you (in terms of you being able to handle it), since it features a very easy-to-use automatic mode. However, it might be more than you need. dSLRs often become a serious investment of not only time but money, as it takes a long time to learn everything there is to know about a SLR, and a lot of money to equip it with all the necessary/wanted lenses and accessories. Lenses especially are not cheap. For this reason alone, you might want to consider one of the high-end prosumer cameras listed above. They usually offer a very versatile lens that covers a wide spectrum of shooting possibilities.

If you narrow your search down to a few cameras, please feel free to post another question and I'll try to help you out in making a final decision. Good luck!