Depends on what you want to do and spend. To play outside you'll need at the minimum an airport base station (you could probably get away with linksys wireless/router basestation, just haven't done it myself) and an iBook with Airport card. The iBook goes for about $1200 for a 12" screen, $1500 for a 14" screen. If you have the money, go for a Powerbook G4 with the 15.2" widescreen (it's worth it) starting from $1995.
Myself, I now have a Powerbook G4 667/512Mb RAM/30Gb HD/CDRW+DVD + Airport and love it ($2995). If you need MS Office 2000/XP compatibility, MS produces a Mac version that is file compatible and then some. I can also access my Windows boxes across the lan (wireless or wired). With a 5+ hour battery life (theoretical, haven't ever used it that long off of AC mail) it comes in a nice 5.4 pound package that includes built-in 56K modem, 10/100/1000 ethernet, 2 USB, 1 Firewire (iLink, IEEE 1392), S-Video, and XGA output.
All in all, I left Wintel for Apple about 5 months ago on a lark and haven't looked back. I can do everything I did on a Win/Linux dual boot Dell Inspiron 7500 with my Powerbook at almost half the weight and it doesn't burn my lap :)
I'm typing this on one, it's a great machine. Apple is reportedly upgrading the Powerbook line next week, so that might be a good time to buy.
Can one of you experts tell me what I would need to have high speed access but play outside in the yard?
A wireless card in the laptop (under $100, and the high-end Titanium comes with one preinstalled), and a wireless router ($150 or less). Basically you plug the router into your existing cable or DSL connection, configure your laptop to use DHCP, and you're set (at least, that's how mine works). You can also set up encryption if you're concerned about your neighbors intercepting your wireless transmissions.