In France you can only get pills dosed at a very small 800 IU (international unit, see: http://www.nafwa.org/vitamind.php) without prescription, but in the US, you'll find some bottles dosing a single pill up to 10 000 IU.
The pills look all the same no matter the dose. They are minuscule yellow balls, but they can be very concentrated.
So "take a lot of Vitamin D" doesn't mean "take a lot of pills". Target an amount of IU, and take exactly what you need for that.
Vitamin D has been found toxic if you take more than 60 000 IU/day for 3 month. You'd have to be quite heavy in your dosing to reach this, but I'd rather share the info.
There is no overdose possible if you get it from the natural source: exposition from the sun. And it's healthier. But as a geek you may see the light of your monitor much more than the one from the sun, and D supplements are incredibly cheap for the huge benefit in energy and mood they provide in the winter.
I take 5 000 UI/day (as Cholecalciferol, so D3), and my doctor already thinks it's a lot since the daily recommended dose here is 200 IU.