I use Apple's OsX at work... (10.5 Leopard) and am an Apple certified System Administrator. I'm not saying this to boast, but to stave off the people who say "You don't know Apples."
Personally, I think Vista is far superior to OsX (flame on...) - but then again, I rarely have problems with the machine I run vista on (to the point that I'm running vista on my MacBook Pro and my Mac Pro; both company issued) and have 600 Macs on the other side...
I think it's unfair to judge a whole operating system based on your experiences with your sister's laptop. No offence intended, but I don't think Vista is the problem... I'm willing to bet there is something installed on the machine that's causing the problems, and not vista.
Similarly, OsX has it problems too... The quantity of virii (viruses?) may be less, but they still exist. Recently, we've found malware and trojans to be on the rise as well... it's the price you pay for increased popularity
![Stick Out Tongue :p :p](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f61b.png)
(oh, and preliminary reports show that OsX user's are more susceptible to phishing attacks*
![Stick Out Tongue :P :P](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f61b.png)
)
Depending on how long you're using your sister's laptop; I have a feeling that you may have trouble going back to XP afterwards... Vista can really grow on you quite quickly...
M.
* Sorry Spike - I couldn't resist!