Is there any problem or limitation (besides the colours quality) if I do it?

Yes you can

You should have no problems if you do. As they say, your software won't be fully optimized for you hardware, but as far as I know and have heard from the general population, software isn't written in a way that it would make a lot of difference performance wise right now anyway. If you want 32bit go 32bit. Otherwise chroot it.

Yes you can install 32 bit distro on AMD64. And presently most applications dont use the full potential of 64-bit platform. So you will not be seeing any major differences.
Only problem I had in the 64-bit distros (I used Fedora) are the driver problems for my video chipset. Wasn't able to start Xserver in the 64-bit, but works perfectly when using a 32-bit distro.

The simple answer is, "Yes". We do this occasionally when we don't have a requirement for the 64-bit capabilities of hardware, especially in areas like our admittedly low-end graphics generation. We tend to use CentOS or Rocks distro's and see no problem. Of course, the traditional caveats exist. you might run into something looking for a 32bit dynamic lib and not have it, and discover that your 64bit OS has sole control over that.

In general, if your requirements are for 32bit apps, consider installing the os as 32bit. That should work fine.

FYI, I just installed 32 bit openSUSE 10.2 on a brand new Dell Inspiron 1501 (Dual core AMD Turion 64) and have noticed no problems.

I used to use a 64bit distro on my system, but ran into several issues with libraries and other dependencies. I now use a 32 bit distro and am more than happy with it. I have not noticed any difference in speed, and am happy with the stability as this is my main box and I need the stability. I plan on eventually going back to a 64 bit distro but am waiting until software can really take advantage of it. I wish I had more money (like everyone else I guess) so I could have another 64bit cpu for a testing box

I have a testing box. It's not a lot of money. A couple hun for a an ABit 939 Mobo and AMD-64 CPU, a gig of memory from TigerDirect for $50 after rebate, a new Ultra box free after rebate. I already had a 500w PSU from some earlier deal when I saw it and I have a number of HDD that I have collected over the years (some even from computers being thrown out). Distros are free so away you go. Deals abound on keyboards & mice so the thoughest item is monitors. Last one I got was with credit card reward points.
That being said - I have tried 32 and 64 bit and don't have problems with any UNTIL I try to start Compiz or Beryl through the KVM switch I use. I have a "work" box that is running 32 bit Suse 10.1 and share the KVM with my AMD-64 play box but the KVM switch can't seem to handle the monitor/graphics matter. But if I ran my own dedicated play box with its own KV&M I don't think I'd have any problems. Of course - I'm not going to do this and I willfind a KVM that will work because I appreciate a little challenge.

OK, thanks.
I'm gonna buy a laptop and maybe with dual core processor, and my doubt was if I had to get a 64-bit distro for that computer (I have only 32-bit distros), for what I've heard about programs for 32 or 64, and also about the performance.

All you have to do is google the name of your distro of choice with "64 bit" to find the iso or similar search at distrowarch.com. Do 64 if you have processor for it.