Regrettably, while Microsoft Windows is undoubtedly a decent operating system (if better ones are not around), it doesn't come with some *very* important tools. Here are some pieces of software that I always get and install on new systems.

PowerArchiver 7-Zip
As strange as it was, Windows didn't come with any zip/unzip tools, even when ZIP is the most widely used archive format on that platform. Instead, for any software distribution, MS relies on their .cab/.msi format and/or self-extracting archives (interestingly, often made with Winzip or pksfx). I first used Info-Zip tools on DOS (or, if long filenames were needed, under Linux - making opening archives on Windows bloody damn hard), but later picked PowerArchiver instead of Winzip because until version 6.0, it was freeware, and was an exact clone of Winzip (plus skin support) - no nag screens =) Recently, I've picked up 7-Zip, which has a different UI, support for many strange formats (including its own), and is distributed under GPL. (I've been told that XP has Zip support out of box though.) ariels recommended ICEOWS.
Regcleaner and Regclean
Look at *NIXes in general: Nice greppable conf stuff in /etc. Look at GNOME: configuration details are kept in directory structure in XML files. Now look at Windows: Huuuuuuge mess of configuration data in a big honkin' binary file no one can really make any sense out of, even with tools. Fortunately, there are tools to mop it up in case it starts to get too crufty. Regcleaner (found at http://www.jv16.org/) and Microsoft's own Regclean help life a lot.
Microsoft Powertoys
This thing is worth the time for at least two tools: Quickres and TweakUI. (XP seems to mostly have these features built in.)
ZoneAlarm
Until Windows XP, Windows didn't come with a firewall. (See Swiss Cheese Security.) ZoneAlarm is pretty good.
some text editor (my choice is SciTE, previously Programmer's File Editor)
Windows only comes with Notepad, which is not a good text editor... PFE is a dream compared to that, and SciTE is definitely a good, modern editor. Some day, I'll fetch and install XEmacs to get an uniform editing experience =)
F-Prot... er, I mean, F-Secure Anti-Virus
I have never had a virus infection, because I've followed common sense... but you can never be too cautious =) (Some say I use F-Secure's anti-virus product only because of patriotism, but, well, from what I've heard it's pretty damn good...)
Ad-Aware, Spybot S&D...
Helps the life in the net somewhat by killing ad site tracking cookies and spyware. If viruses have never been a threat, adware/spyware is far more deadlier and insidious.

Of course, then there's a bunch of highly cool Windows apps, but those aren't really "basics"... I must see how nice installation help InCtrl5 is. =)

Some of the less basic include Mozilla browser (MSIE is ludicrous, wake me up when it finally supports trivial CSS 1...), and Winamp. And, for an *NIX geek like me, Cygwin environment to get that familiar bash prompt and Perl. And gcc. You just can't live without gcc. Mmm.

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