I'm a  newbie and this might be simple but am going around in circles for now. I want to get rid of the DeclarativeCatalog Part and implement my own system for adding my custom web parts to a page. I'm aware that I can use the WebPartManager object to add Web Parts, and the syntax off the WebPartManager object is:

WebPartManager.AddWebPart(WebPart, WebPartZone, ZoneIndex)

My question is how to get the "handle" to the given custom Web Part. Ex: 

<%@ Register TagPrefix="psp" TagName="ButtonBar" Src="./UserControls/ButtonBar.ascx" %>

Dim ButtonBar1 As WebPart

 You can try something like this..should work.

Dim wpm as WebPartManager = WebPartManager.GetCurrentWebPartManager(Me.Page)
Dim gwp As GenericWebPart = wpm.CreateWebPart(LoadControl("UserControls/ButtonBar.ascx"))
wpm.AddWebPart(gwp, pspzone1, 0)

Thanks Matt this was a big help....

I'm getting this runtime error though in the bolded section below:

"The specified control of type 'ASP.PsPortals_ButtonBar_UserControl' does not have an ID."

        Dim wpm1 As WebPartManager = WebPartManager.GetCurrentWebPartManager(Me.Page)
        Dim gwp As GenericWebPart = wpm1.CreateWebPart(LoadControl("./UserControls/ButtonBar.ascx"))
        wpm1.AddWebPart(gwp, pspZone_LogView, 0)

I tried adding a ClassName to the UserControl, (as per example in MSDN: http://msdn2.microsoft.com/en-us/library/c0az2h86.aspx), but that did not clear the error. Do you have any idea what "ID" it is talking about?

Thanks much again I think I'm close...

 Ok....I got it working - I had to break out the creation of the webpart into a seperate step and assign an ID to it. Not completely sure why, but it works just fine now. Final code was:

ButtonBar1 = LoadControl("./UserControls/ButtonBar.ascx")

ButtonBar1.ID = "ButtonBar"

 That's what I would suggest doing.  The Control needs an ID in order to be turned into a WebPart.
So you will have to separate the code into the 2 lines like you did.
Same will need to be done if you are loading a webpart class as well i believe.