Bearing in mind that, according to the corporate media, US troops have fired on Iraqi demonstrators today, killing a number of them, it would seem that holding US and British "liberators" legally accountable is only too necessary.
It probably won't happen, though.

Basically, this won't happen.

There are four possibilities that I (as an international law layman) know of here.

1. Prosecution at the International Court of Justice
2. Prosecution at the International Criminal Court
3. Prosecution in Belgium under special Belgian legislation
4. Prosecution in the US

Solution 1 will not work as the International Court of Justice only allows countries to press charges against other countries - not against individuals.

Solution 2 will not be possible as - although individual officers, soldiers, politicians etc. can be prosecuted here - Uncle Sam has not signed up, and is unlikely to ever do so.

A number of Iraqis are apparently hoping to press charges in Belgium using solution 3. However, the Belgian legislation that underpins this is extremely controversial, and the US has already threatened "diplomatic consequences" should charges be made. The Belgian state will probably twist its own judges arms and make sure nothing happens.

Solution 4 we can forget. I don't know if there is a precedent, but you can well imagine under the current patriotic mania that reigns in the US that lawyers and judges ready to take on something like this would be extremely thin on the ground. Plus, for all I know, prosecution for war crimes is probably explicitly forbidden by US law.

Unfortunately, this is a realistic assessment of the chances of US soldiers, officers or politicians being tried for war crimes in Iraq. As ever, the US commits the crimes and the victims are left to pick up the pieces.