In answer to Stephen Harris, who's seeking to finally enter the computer age and is looking for the right machine for him, this is a huge subject, and largely a matter of personal preference.
To buy a machine, most people head for Akihabara, as Ken wrote last week.
Choosing a make and model comes down to the buyer's taste -- I won't be parted from my (by now dinosaur-like) LC630 Wordperfect Mac, my husband is newly attached to his Microsoft-loaded Mebius.