shall i need a special microphone to talk in SL

[Rolig Loon]

Any one will do, although clearly you'll get better sound with a good microphone than a crummy one.  Some people prefer to use a headset that has a microphone and earphones so that they can keep their hands free and hear conversation well.  Personally, however, I have never bothered with any microphone and neither have most of the people I have known in SL for the past eight and a half years.  Typed chat works fine and you don't need any special equipment.

[Rolig Loon]

Any one will do, although clearly you'll get better sound with a good microphone than a crummy one.  Some people prefer to use a headset that has a microphone and earphones so that they can keep their hands free and hear conversation well.  Personally, however, I have never bothered with any microphone and neither have most of the people I have known in SL for the past eight and a half years.  Typed chat works fine and you don't need any special equipment.

[Rhonda Huntress]

You may use any mic that works with your PC.

As for need, i have needed to use a mic exactly twice in about 10 yrears and one of those times we went back to the keyboard anyway.