Which version of Visual Basic can I use?

You can use these algorithms in all versions of Visual Basic.

The first edition was written in VB3 and the VB3 source code from that edition is included on the second edition's CD-ROM in addition to revised VB5 code. The new features in VB6 did not add much that affects these algorithms so the CD-ROM includes VB5 code but not VB6 code. The programs run in VB6 without modification.

Some concepts are easier to understand using the object references and collections introduced after VB3 so the code in the text is aimed at programmers using VB4 and later. Chapter 13 covers object-oriented paradigms that are difficult to implement in VB3.

The best algorithms depend on fundamental concepts not peculiarities of a particular version of a language, so all of these algorithms should run in VB6, VB7, and even later versions of Visual Basic.

I have not yet translated the algorithms into VB.NET but they should require few changes. The programs thath demonstrate the algorithms may need some changes because VB.NET handles controls differently.

Should I buy the new edition if I already have the first edition?

It depends. If you are working in VB3, you probably do not need the new edition. It covers many topics assuming you can use the classes introduced in Visual Basic 4.

If you are using Visual Basic 4 or later, you may want to buy the second edition. Many of the algorithms in the first edition are easier to understand using classes. Chapter 13 in the second edition also explains object-oriented paradigms not possible in Visual Basic 3 and not discussed in the first edition.

If you are using VB.NET, you may have to do a little translation to make the algorithms work. The second edition will be a lot easier to translate than the first edition.