64 bit and 32 bit
Most computers run in 32 bit. If you have a standard Intel machine (as of January 2006) then you probably do not need to worry about this.
Which is better
A 64 bit processor is the way of the future. If you are conservative, I would still recommend staying with 32 bit because there are so many of them. Meaning they are better tested and the computers are far cheaper. Within 10 years I expect most computers to be 64 bit however I believe that between now and then the average person will have another 2 computers (one every 5 years) so stick with the common hardware unless you really have a reason.
The bottom line is that for free software it is not that important. Code can be converted between the two because it is source code so that most things 'just work'. The unfortunate thing is that it is actually a little tricky converting some programs from 32 to 64 bit and therefore some programs cannot run in native 64 bit mode. They can run in an emulated mode but this will be a little slower. There is even the case when code that works in 64 bit actually runs slower because of the magic in the processor differences.
What is it really
32 bit and 64 bit is really the size of a chunk of memory in the computer. A 32 bit computer has a word size of 32 bits, this limits the memory to a very very large number. A 64 bit computer will handle a literally enormous amount of memory.
We are moving towards a world where information is stored in a terabyte. A few of these will store all the programs of your favourite TV station for a number of years. When you are moving this amount of data and compressing it to store it more efficiently then you need the extra power 64 bit allows.
How to make 32 bit work on a 64 bit machine
At this time, those with a 64 bit processor have the option of installing the 64 bit version of Ubuntu. Not all software is available in the 64 bit environment. In particular non-free items are usually 32 bit. For example the Flash plugin is a 32 bit program.
Some programs can be run in the 64 bit version of Ubuntu by using the 32 bit libraries.
You can use [:Rootsudo:sudo] and [:AptGetHowTo:apt-get] to install these libraries.
sudo apt-get install ia32-libs*
One can also use the [:SynapticHowto:Synaptic package manager] to install the 32 bit libraries.
Another option is to create a 32 bit environment with [:DebootstrapChroot:chroot]