From what I have learned of the ULN2803 (never heard of it before today), which is the chip on the Velleman board. It can only 'sink' current ( ie. ground it ), throughout this thread, I have assumed that the board could 'source' ( ie. supply it. ) My fault entirely. Mind you, not to worry. From what I can gather;
Whatever is present on one of the 8 screw terminals on the velleman board will be connected to the 'clamp' terminal when you click the mouse on the appropriate bit of software.
As I see it, you have the two red horizontal ( nearly ) lines the wrong way around.
Believe me, If my local Maplin branch had one of these things in stock, I'd have bought it about 3 days ago and made it, tested it and sent you exact details, diagrams, pictures, video, video in 3-D...etc
Don't worry, you wont melt your PC.
Though, thoroughly check that your relay board works first.