Depends on the nature of the insertion. As long as expression of the targeted gene doesn't rely on the presence of an enhancer or any other chromatin-structure-mediated control mechanism within that intron, the insertion may make no difference to the gene promoter activity. As for the inserted DNA, it would most likely be spliced out and degraded as normal unless it interfered with spliceosome formation. If it carried features allowing translation, such as IRES, Kozak and polyA sequences, or a splice acceptor to tag onto preceeding exons (such as in gene trapping), the targeted gene would be disrupted and fail to translate. Disrupting the expression of the gene could well have an effect on the promoter too, in that the gene product may regulate its own expression.