Windows 98 & ME, 2000
We live in a disposable society, so when Microsoft throws one of it’s operating systems out of support, it’s time to upgrade or buy new. Microsoft no longer support your operating system, it is vulnerable to attack (only if connected to the internet), compatibility problems will become more of an issue for software and hardware upgrades.
Windows XP (Home and Pro)
Make sure you install all relevant Microsoft patches (if you don’t know what is relevant, install everything), also be aware of other software installed on your system that may need upgrading due to vulnerabilities. This can include driver and firmware updates to hardware, internet plug-ins like Shockwave or Flash, or software updates like Adobe Reader, CD authoring software but especially your Internet Security software. Why not try this site which claims to find updates for 4200 applications -Secunia.com
There are still problems with a lot of the drivers and software compatibility issues in Vista, but they are becoming available all the time, so if you are worried about upgrading to Vista, check the compatibility wizard to see if you’ll have problems with any drivers or software on your system. Microsoft Upgrade Advisor