Having never owned a lap top before excuse my ignorance

Was thinking of getting a lap top with some sort of internet capability. Ive heard of wi-fi etc etc but not sure what it all means. Was briefly explained to me but my eyes glazed over, something along the lines of hot spots needed, no monthly charge but billed per minute of usage?

Also, Ive stumbled across a site about a vodafone 3g card that plugs into lap tops. Prices:

Anticipated usage Recommended retail price for datacard Monthly cost Promotion Data included (per month)
Medium £150 £23.50 50MB
High £130 £53.00 300MB
Power £100 £99.99 1000MB

Ive seen these cards on ebay for a lot cheaper than the rrp, are these likely to work ok and are legal? Im assuming that Id be a medium user, but can anybody quantify what a mb is in laymans terms, ie in terms of hours a day in a month for surfing places like scoobynet on the medium plan 50 mb?

Is this a truely mobile service, like will I expect many black spots in coverage?

 

1 megabyte is equivalent to approx 1200 wap pages or 20 web pages, 100 emails without attachments or 10 emails with a one-page attachment.

What ive found at last