If memory serves me correctly, the technology behind x10 was developed by a British scientist. It is actually older technology that had a patent and when the patent ran out X10 was developed as standard so different manufacturers could make devices that can recognize the same language just like TCP/IP is a standard language (protocol). Only X10 is very simple in what it can do. To represent a binary digit of 1 a 120 kHz burst if applied for 1 millisecond where the sine wave crosses zero. Since our frequencies are different, meaning power in the use is at 60hz and power in the UK is at 50hz, it's not only a matter of voltage difference, it's a matter of timing the burst of data. Otherwise it will get lost in the noise of the active power cycle. But you are in luck because X10 is well documented and easy to control, so it is easy to code in VB (I would imagine). There is a Dutch distributor of 220v X10 products.

Marmitek BV
P.O. Box 4257
5604 EG Eindhoven
Netherlands
Tel: +31 40 2122 831
Fax: +31 40 2128 232

I didn't verify this but if it's a dead-end I will continue to ask around...