Hi,

Getting rid of the arrows is just a property setting, setting NumericUpDown.HideButtons = true.

Customizing the control to make it nullable is a bit more effort, which has more than one solution. The decision you need to make first is what datatype you want the value property to be, as decimal types in .NET don't accept null values so that type will not work for you directly. 

I built a Skinable NumericUpDown control as a demo case for you where I make the Value property of type object and then make some changes to the control, both server-side and also how it is rendered. The changes server-side should be obvious when you look at the sample. The changes client-side (the XSLT) may not be as obvious, but the idea is that the control will render an extra flag notifying the client-side if it should be interpreted as null or not. If null, then the xslt will render an empty control (no value) but if false, it will render the value as it usually does. This may not be 100% accurate, but for the most part I think it works. 

The demo can be seen from either the Case studies section in the custom controls article, or directly from the NumericUpDown article.

Hope this helps,

Palli