Best way to pass a connection object among forms?

Background: I'm rewriting a VB6 app that used MS Access for data storage to one that uses VB.NET and MS SQL Server.

I'm curious as to the best way to pass a connection among the different forms in my application that need a connection to the database. Right now I've built a class to manage the connection string to pass that between forms in a secure manner:

Public Class LoginCredientials

    Private uname As String

    Private password_hash() As Byte = {0}

    Private server_name As String  'not used in access style databases

    Private dbname As String

    Private st As ServerType  'enum that would allow for different connections

    Private tdes As TripleDES 'encryption class to encrypt password in memory



    Public Sub New()

        uname = ""

        server_name = ""

        dbname = ""

        st = ServerType.stNotDefined

    End Sub

    Public Sub New(ByVal Username As String, _

                   ByVal Password As String, _

                   ByVal ServerName As String, _

                   ByVal DatabaseName As String, _

                   ByVal ServType As ServerType)

        tdes = New TripleDES

        uname = Username

        password_hash = tdes.Encrypt(Password)

        server_name = ServerName

        dbname = DatabaseName

        st = ServType

       tdes = Nothing

    End Sub



    Public ReadOnly Property Server_Type() As ServerType

        Get

            Return st

        End Get

    End Property

    Public ReadOnly Property CompanyName() As String

        Get

            Return dbname.Remove(0, 4)

        End Get

    End Property

    Public Property UserName() As String

        Get

            Return uname

        End Get

        Set(ByVal value As String)

            uname = value

        End Set

    End Property

    Public Property Password() As String

        Get

            tdes = New TripleDES

            Return tdes.Decrypt(password_hash)

            tdes = Nothing

        End Get

        Set(ByVal value As String)

            tdes = New TripleDES

            password_hash = tdes.Encrypt(value)

            tdes = Nothing

        End Set

    End Property

    Public Property ServerName() As String

        Get

            Return server_name

        End Get

        Set(ByVal value As String)

            server_name = value

        End Set

    End Property

    Public Property DatabaseName() As String

        Get

            Return dbname

        End Get

        Set(ByVal value As String)

            dbname = value

        End Set

    End Property



    Public Function GetConnectionString() As String

        Dim cstring As String = ""

        tdes = New TripleDES

        Select Case st

            Case ServerType.stSQLServer

                cstring = "User ID=" & uname & ";" & _

                        "Password=" & tdes.Decrypt(password_hash) & ";" & _

                        "Initial Catalog=" & dbname & ";" & _

                        "Data Source=" & server_name

        End Select

        tdes = Nothing

        Return cstring

    End Function

End Class

I had been passing a reference to my object to any of my forms that needed a connection to the database like so:

'in the form declaration

Private myLC As LoginCredientials

Public Sub New(ByRef lc As LoginCredientials)

    InitializeComponent()

    myLC = lc

End Sub

And then I would create a new connection object, did what I needed to do, and then closed the connection and destroyed the connection object. When I've done this before long ago in ADO with VB6, the process created by the connection was killed when the connection object was destroyed, but that doesn't appear to be the case anymore. Now every time I create a new connection object and connect to my server, a new process is created and then put to sleep when I close my connection. After a while the server will start refusing connections until I log in and kill all the processes my app created. Obviously this isn't being done right, and I would like to learn the right way.

Would it be better to simply pass the same connection object by reference (or inside a wrapper class) among my forms, leaving the connection object open?

What is the correct way to close my connection so that I don't eventually get a bunch of sleeping processes on my SQL server? Is there a setting in SQL server I can adjust to automatically kill processes after a certain period of inactivity?

Would you consider encrypting the password in runtime memory overkill?

Thank you for any help. :)