有限公司可否只有一位股東？

Yes, a limited company could have a single director and a shareholder. It is a violation of law if the Memorandum and Articles of Association still stated that there should be at least 2 members or directors to transact a business of the company but in fact you have 1 person.
As your company is long established. You should arrange a shareholders’meeting to approve and adopted a new version of Memorandum and Articles of Association with the clause allowing the number of directors and shareholders could be 1. After that, the shares from the other party to be transferred to your boss and at the same time the other party should resign as a director of the company.

2009-06-20 17:54:41 補充：
Companies (Amendment) Ordinance 2004 (30 of 2004).

S. 153 in http://www.legislation.gov.hk/eng/home.htm

-幾年前香港公司法例是可以一個股東
-但都是要根據公司的章程, 如當年成立是指明兩個股東, 則要股東通過決議再改章程 M & A
-做轉股文件去打stamp duty, 取消董事文件, Resolution, etc
-公司帳目都要記帳
有限公司太多關於法例上了, 一般都是找會計師, 律師等follow的, 如不明白可來信給我.