As far as I can tell, the SmartQ V5 comes with three operating systems installed (Linux, Windows CE and Android), so there should be no need to install Windows or any other operating system. That said, neither Windows CE and Android were really designed for this device, and can be a little difficult to use, so you'll probably want to stick with Linux. I'm not sure about installing antivirus. Like most mobile devices, the majority of viruses shouldn't be an issue, since they target Windows, but that doesn't guarantee safe browsing. As for the battery, I don't think you would need to replace it. You can recharge it with an AC adaptor.
The SmartQ V5 looks like a good device for occassionally browsing the internet, checking emails, etc. I think it can take an SD card for expandable memory, which is a useful feature. The linux OS is very easily customised and allows a lot of flexibility with software, but might be a little tricky to use if you're not used to it, at least for a while. It's also not a very capable gaming device.
There are other devices with similar capabilities that you may want to consider. The best one for you depends on your needs.
You might want to consider:
- Datawind's PocketSurfer3 is similarly priced. It has an easy to use QWERTY keyboard, and takes advantage of GPRS coverage. I don't think it has WiFi capabilities though, although Datawind claim that "FREE USAGE included in the price of the PocketSurfer3 is 30 hours of usage per month free for the first year, more than enough for the average user". If you want more usage per month or after a year, you have to pay for the service. I don't know much about its software, but I doubt there is much room for customisation.
- An 8GB iPod touch from Apple is fairly cheap and offers simple, hassle free browsing, with plenty of other apps available, for gaming, etc. However, the Safari browser doesn't have a flash player, and you are very restricted in terms of customisation and installing software not available in the app store. It does have very useful apps for email and YouTube though, and popular social networking apps like Facebook and Twitter are available for free.
The only device I've actually used of these three is the iPod touch, and it's served me well. It's a more than capable browser with some useful features, and I also use it as an mp3 player and to play games when I get bored.
Any questions and I'd be happy to answer. I hope I helped at least a little bit.