Williams takes over from Colin Charvis, who is out of action with a dislocated finger.
He turned the job down before the World Cup, but has happily taken the responsibility this time.
"I made it clear when I did not take it for the World Cup that it was not something that I did not want to do," he said.
"But it was not right for personal reasons at the time.
"It showed in the World Cup that Colin had done a great job. He is still the captain and I am only stepping in for one job while he is injured."
Williams is eager that the Welsh take the momentum from their win over Scotland to Dublin, especially after four successive defeats away to the Irish.
"Lansdowne Road is a tough place to play and is another step up from last week," added Williams.
"I have fairly mixed memories of Dublin. The last game (a 35-12 2003 World Cup warm-up defeat) was especially painful because we lost heavily.
"It is a difficult place to play and sometimes it looks like they have got more than eight forwards on the park.
"They are a very dangerous sides. We don't fear them but you have to be wary of Ireland because they have got a very good recent record at Lansdowne Road.
"They are a team who have been together for about five years so they are used to each other.
"We have been capable of beating sides in the past but have failed to do so. We have to look at getting some consistency like Ireland have done over the last three or four games."