Answer A) Apple never sold a good laptop. Buy a new Latitude, ThinkPad, or if you hate money, HP Elite. Mac OS X runs on desktops.
Answer B) (probably the answer you want) The "MacBook" with no Air or Pro on the end was an Intel system all the way from its introduction in 2006 to its discontinuation in 2009 or 2010.
If you absolutely MUST have a white laptop, I would go for the newest MacBook (unibody) that you can find. The directly previous model that was still discrete-bodied but had the GeFORCE 9400m graphics should also have a bit of life left in it, and has the advantage of a swappable battery, which can be nice if you plan on keeping the machine a very long time.
When shopping for Macs, keep in mind that there's about a three year window between when a machine was first sold and when it's really considered to be a good choice for anybody who wants to keep up with the Mac platform. Honestly, even if you can find a Penryn unibody Macbook from 2009 or 2010, it'll be a good computer for a while, but it wont' be a good Mac for very much longer. Mountain Lion, coming out in a few weeks, is likely to be the last version of the OS that supports these machines. Plus, Mac laptops are famously finnicky, especially pre-unibody machines, and having a warranty (or just having one that somebody hasn't done who-knows-what to) is the way I'd prefer to do it, if you can swing it.
Answer C) (when budget is the most important concern) Please do not buy an iBook. There's no reason to have an iBook here in 2012 unless you need Classic Mode for OS 9 applications, or you have one of the very first models, 500MHz, or 600MHz with ATi Rage graphics. (Every other white iBook had significant manufacturing defects or design flaws.)
Answer B) (probably the answer you want) The "MacBook" with no Air or Pro on the end was an Intel system all the way from its introduction in 2006 to its discontinuation in 2009 or 2010.
If you absolutely MUST have a white laptop, I would go for the newest MacBook (unibody) that you can find. The directly previous model that was still discrete-bodied but had the GeFORCE 9400m graphics should also have a bit of life left in it, and has the advantage of a swappable battery, which can be nice if you plan on keeping the machine a very long time.
When shopping for Macs, keep in mind that there's about a three year window between when a machine was first sold and when it's really considered to be a good choice for anybody who wants to keep up with the Mac platform. Honestly, even if you can find a Penryn unibody Macbook from 2009 or 2010, it'll be a good computer for a while, but it wont' be a good Mac for very much longer. Mountain Lion, coming out in a few weeks, is likely to be the last version of the OS that supports these machines. Plus, Mac laptops are famously finnicky, especially pre-unibody machines, and having a warranty (or just having one that somebody hasn't done who-knows-what to) is the way I'd prefer to do it, if you can swing it.
Answer C) (when budget is the most important concern) Please do not buy an iBook. There's no reason to have an iBook here in 2012 unless you need Classic Mode for OS 9 applications, or you have one of the very first models, 500MHz, or 600MHz with ATi Rage graphics. (Every other white iBook had significant manufacturing defects or design flaws.)