If you have the cash to spring for antivirus (or have to because you are a business and have lots of computers) try out Kaspersky and ESET Nod 32.
On the Mac side, I’d stay away from both of the Norton and McAffee products. Both have a reputation for causing weirdness that should have also been earned on the Windows side as well (I’ve run into some totally showstopping bugs over the last few years). If you NEED an antivirus there is a graphically-driven version of ClamAV for the mac that is free, and will scan files.
For home gear I now generally recommend stuff from Netgear. Their current boxes seem to generally work more reliably than equipment from Linksys or D-link (though they generally also work well), and are readily available. They also tends to upgrade fairly easy.
If you’re willing to spend the extra money, the Airport WAP/routers fromApple are high-quality pieces of equipment with excellent security, signal strength, and ease-of-setup features, as well as allowing their use as a repeater, and a decent Windows/Mac print server for USB printers. The repeater functionality is especially slick and well done. Last but not least, the Time Capsule allows for wireless home storage and across-the-network backups (for Macs). Otherwise, I’d usually go for a Netgear.
Windows: IE8 is a huge improvement in many ways. It is somewhat safer from hijackings, has tabs for browsing, and best of all for all too many people I’ve known, finally fixes a printing bug that would cut off the right side of wider web pages.
That said, in combination with all of the various security updates and antispyware and firewalls and such, Windows starts running like a crippled turtle with IE7 on it unless you have a lot of RAM. 512MB, even 756MB, no longer cuts the mustard. 1GB on a Vista machine is asking for trouble.
So if you want a browser that won’t punish your system as much, and is still more secure, nevermind more extensible, do yourself a favor and use Firefox or Chrome wherever you can.
Firefox is a solid browser with support for many useful plugins, but getting away from its origins as a small, light, standards-compliant alternative to IE. Chrome is a browser provided by Google that uses the same “webkit” rendering engine as Safari (also available for Windows) but with an emphasis on speed and a minimalist interface that I wish Firefox would emulate.
Mac: A matter of taste. While there are other good options available such as Camino, you really can’t go wrong with either the built-in Safari, Chrome (intel macs only), and Firefox for those occasions where Safari just won’t work, or vice versa. Firefox is slower but far more flexible, and on the newer intel-based Macs, the differences are far less noticeable.
As much as is humanly possible. Neither an up-to–date copy of XP nor OSX run comfortably with less than a gigabyte of RAM. Two Gigabytes or more are recommended for OSX or Vista. Check out 18004memory.com for good prices and a great return policy. Another good place to check out is crucial at crucial.com.