Colingl:
I would check with the laptop manufacturer, most of the well known ones do car kits, so should be Ok on 24v as well but as Lostpup says, worth checking.
Iād be very surprised if a standard car adaptor will run from 24 V. Itās more likely to either blow a fuse in the adapter (or the truck), or maybe even overheat and catch fire.
Of course, check the specifications, and you might be lucky and get one that supports 24 V.
If youāre always going to use it in the same truck, then find out what your truck has got - if thereās 12V sockets thatāll provide enough current, then Iād suggest using one of them with a standard car adapter. If you have to use 24V, then look to see if the car adapter supports 24 V; if it doesnāt, youāll need a 24 V - 240 V inverter, plus the standard mains power supply.
Scan - www.scan.co.uk are worth a look as weel. Dealt with them quite a bit and are very reliable. Best bit is they have a todayonly page where you can sometimes pick up a bargin 
In my experience, Scan are great, until something goes wrong (after theyāve got your money). After that point, getting hold of customer services is next to impossible.
I once bought some RAM from them which turned out to be faulty - fair enough, it happens sometimes. However, I then spent the next month and a half trying to get hold of Customer Services. They ignored all emails and submissions to the web form. The telephone line was permanently engaged, and I tried all times of the day and week, calling pretty much every day. Itās not that they kept me in a queueing system; I couldnāt even get into a queue, as the line was just engaged.
I finally got a response when I emailed one of the company directors in response to his article on the website saying āweāre focussing on customer serviceā. My response? āYeah, right.ā It was sorted out, but I shouldnāt really have to resort to sending snotty mails to company directors just to get a faulty product replacedā¦
Their products and prices are good, but their service stinks. Of course, things could have changed since then.
PC World - always good for a laugh if you ask them even the slightest techy question they flap
Maybe its just me though

PC World used to be seriously overpriced, but theyāre not so bad now. However, the staff havenāt improved. They know about as much about computers as many TMs know about driving⦠
PC-World-staff-baiting has been proposed as an Olympic sportā¦

Iāll never forget the time I went in and asked if they had a ānull modem cableā, and the salesdroid said āParallel or serial?ā 
Iāve never used Overclockers. Iāve used dabs a few times, and never had any problems, but Iāve never had to contact Customer Services for anything eitherā¦
Youāll probably have to use a USB-based TV card, as your laptop wonāt take a PCI one. If you want some advice, feel free to PM me.