The International Herald Tribune reports that four of Fr Ly's associates were also jailed, one to a six-year term.
Another two activists, lawyers Nguyen Van Dai and Le Thi Cong Nhan, are due to go on trial later this month.
"We are worried by this undemocratic action which we perceive as a gross violation of civic rights," said an open letter to the Vietnamese prime minister, president and parliamentary speaker, signed by Havel and dozens of other prominent Czech personalities.
"We express our solidarity with the convicts and demand an immediate release of the convicts and the arrested," the letter said.
Roman Catholic Bishop Vaclav Maly, Rabbi Karol Sidon or Senator Petr Pithart - dissidents under the former communist regime - are among the letter's signatories.
Havel, other former Czech dissidents, call for release of jailed Vietnamese activists (International Herald Tribune, 9/5/07)
LINKS (not necessarily endorsed by Church Resources)
Vaclav Havel (Wikipedia)
Nguyen Van Ly (Wikipedia)
Amnesty International - Vietnam
Suffering witness to faith, says jailed Vietnamese priest's brother (CathNews, 20/4/07)
Eight years jail for Vietnamese priest (CathNews, 2/4/07)
Benedict visit on cards for Vietnam (CathNews, 13/3/07)
Vietnamese democracy priests arrested (CathNews, 21/2/07)
Vietnam PM in first Vatican visit (CathNews, 24/1/07)
Vietnam releases dissident priest (CathNews, 23/2/05)
Vietnamese freedom fighter priest arrested again (CathNews, 21/5/01)
10 May 2007