There are a couple of way to do this:
Click Open and select the file. If you are importing a DWG file, click Options, and select Import options, and click OK. Click Open to start the DWG File wizard.
In the Layers and Objects Import Options dialog box:
Select the layers to translate.
Click Next.
In the Import Destination Options dialog box:
In Destination for 2D data, specifyTitle Block.
Set the destination directory for the new file.
Select a drawing template.
Click Finish to create the file.
OR:
Open the Tb in acad,
Place everything on the 0 layer,
Copy the TB to the windows clipboard (CRTL + C)
Start a new TB in Inventor
Paste (CTRL + V) the ACAD TB in
Update the text tags to use the appropriate iProperties as needed,
Save TB definition.