we have HP's at work, and they are always breaking. IBMs are a nice balance between sturdiness, and perfrmance. i really like the lenovo think pad r61. i have no experience with dells, but i have always heard that they suck.
anyway, if you are looking for the most "reliable" laptop, you have to go with mac. they are the best. no viruses, sturdy, fast, and they are so sexy looking.