Public Function Add ( _
    urlOfFile As String, _
    file As Byte(), _
    createdBy As SPUser, _
    modifiedBy As SPUser, _
    timeCreated As DateTime, _
    timeLastModified As DateTime _
) As SPFile

Dim instance As SPFileCollection
Dim urlOfFile As String
Dim file As Byte()
Dim createdBy As SPUser
Dim modifiedBy As SPUser
Dim timeCreated As DateTime
Dim timeLastModified As DateTime
Dim returnValue As SPFile

returnValue = instance.Add(urlOfFile, file, createdBy, modifiedBy, timeCreated, timeLastModified)

public SPFile Add (
    string urlOfFile,
    byte[] file,
    SPUser createdBy,
    SPUser modifiedBy,
    DateTime timeCreated,
    DateTime timeLastModified
)

Dim site As SPSite = SPContext.Current.Site
Try
    Dim srcFolder As SPFolder = site.AllWebs("MySourceWebSite").GetFolder("MySourceDocLib")
    Dim destFiles As SPFileCollection = site.AllWebs("MyDestinationWebSite").GetFolder("MyDestinationDocLib").Files

    Dim srcFile As SPFile
    For Each srcFile In  srcFolder.Files
        Dim destURL As String = destFiles.Folder.Url + "/" + srcFile.Name
        Dim binFile As Byte() = srcFile.OpenBinary()
        Dim userAuthor As SPUser = srcFile.Author
        Dim userModified As SPUser = srcFile.ModifiedBy
        Dim created As System.DateTime = srcFile.TimeCreated
        Dim modified As System.DateTime = srcFile.TimeLastModified

        Dim newFile As SPFile = destFiles.Add(destURL, binFile, userAuthor, userModified, created, modified)

        Dim fileItem As SPListItem = newFile.Item
        fileItem("Created") = created
        fileItem("Modified") = modified
        fileItem.Update()
    Next srcFile
Finally
    site.Dispose() 
End Try

SPSite oSiteCollection = SPContext.Current.Site;
SPFolder oFolder = oSiteCollection.AllWebs["SourceWebSite"].GetFolder("SourceDocLib");
SPFileCollection collFiles = oSiteCollection.AllWebs["DestWebSite"].GetFolder("DestDocLib").Files;

foreach (SPFile oFile in collFiles.Files)
{
    string strDestUrl = collFiles.Folder.Url + "/" + srcFile.Name;
    byte[] binFile = oFile.OpenBinary();

    SPUser oUserAuthor = oFile.Author;
    SPUser oUserModified = oFile.ModifiedBy;
    System.DateTime dtCreated = oFile.TimeCreated;
    System.DateTime dtModified = oFile.TimeLastModified;

    SPFile oFileNew = collFiles.Add(strDestUrl, binFile, oUserAuthor, oUserModified, dtCreated, dtModified);
    SPListItem oListItem = oFileNew.Item;
    oListItem["Created"] = dtCreated;
    oListItem["Modified"] = dtModified;
    oListItem.Update();
}