(Today’s Halacha is based on a Shiur delivered by HaGaon Rabbi Gidon Ben Moshe of Jerusalem)
There is a debate among the Rishonim (Medieval Halachic scholars) as to whether the restrictions of the week of Tisha B’Ab apply when Tisha B’Ab is observed on Sunday, as it is this year (5772). According to one view, the restrictions must be observed throughout the week before Tisha B’Ab, whereas the other opinion maintains that since Tisha B’Ab begins right after Shabbat, there is no "week of Tisha B’Ab" and thus these restrictions do not apply at all in such a year. The Shulhan Aruch cites both views, but he mentions the stringent view as "Yesh Omerim" ("Those who say") and the lenient view as "Setam" (without any title). This indicates that the Shulhan Aruch sides with the lenient view, that when Tisha B’Ab begins on Mosa’eh Shabbat, the restrictions of the week of Tisha B’Ab do not apply.
As such, it is permissible to shave, take haircuts, take hot showers, and wear freshly-laundered clothing throughout the week before Tisha B’Ab in such a case.
One must remember, however, that even when Tisha B’Ab is observed on Sunday, freshly-laundered garments may not be worn on the day of Tisha B’Ab itself. On Mosa’eh Shabbat, of course, people will still be wearing their clothes from Shabbat, but on Sunday, the day of Tisha B’Ab, people will generally put on new clothing. That clothing which is worn on Sunday must not be freshly-laundered, for although there is no week of Tisha B’Ab when wearing fresh clothing is forbidden, it is still forbidden to wear fresh clothing on Tisha B’Ab itself. Therefore, even in a year when Tisha B’Ab falls on Sunday, one must prepare clothing for Tisha B’Ab day by wearing a change of clothing beforehand, such as on Friday. The clothes should be worn for a brief period until they absorb a bit of perspiration, so they will not be fresh on Sunday.
Additionally, even though it is, strictly speaking, permissible to shave during the week before Tisha B’Ab when Tisha B’Ab is observed on Sunday, several Poskim rule that it is proper not to shave before Shabbat. In order not to appear cleanly-shaven on Tisha B’Ab, it is preferable to refrain from shaving on the Friday before Tisha B’Ab (and there is room to consider refraining from shaving even on Thursday). This is the ruling of the Ben Ish Hai, Rav Haim Palachi, Hacham Ben Sion Abba Shaul, and Hacham Ovadia Yosef.
The custom of the Arizal (Rav Yishak Luria of Safed, 1534-1572) was to abstain from shaving, haircutting and eating meat throughout the three weeks from Shiba Asar Be’Tammuz through Tisha B’Ab. This practice is not required according to the Halacha, and is rather a stringency that may be followed by those who are sincerely driven to do so.
Summary: When Tisha B’Ab is observed on Shabbat, it is permissible to wear freshly-laundered clothing during the week before Tisha B’Ab, but not on Tisha B’Ab day, and therefore one must prepare a change of clothing for Tisha B’Ab by wearing the clothing for a short while beforehand. It is also proper in such a case to refrain from shaving on the Friday before Tisha B’Ab.