While it is nice that there exists some external verification (from non-Christian writers and archaeology) that lend credence to some of the historical claims of the Bible, we need not forget that there are some Christians who can provide testimony to the NT's historicity, at least in part. Again, I'm not trying to "prove" the Bible is historically accurate, merely compiling arguments as to why it may be rational to believe so. The testimony of the early church is another block in that particular support structure.
This additional testimony may be thought to be more biased, ergo not reliable, in regards to providing evidence to the texts' accuracy. As far as arguments go, this one is likely to garner a sympathetic audience. We often cry foul when a study is funded by an organization that stands to benefit from the results - we're not huge fans of conflicts of interest, real or perceived.
However, this argument shouldn't really stand in our way from accepting the testimony of the church fathers as possibly being true. When evaluating an argument, it would be folly to disregard what is offered simply because of the beliefs of the person offering up the argument. Instead, the argument should be judged on its merits, with a person's credibility being but a part in the evaluation of evidence they put forth. As this relates to the issue at hand, I think it reasonable to put the burden of proof on those who'd claim the early church fathers were mistaken or lying. Barring that, there is no cause to dismiss their testimony simply because they were Christian. After all, perhaps they were Christians because they knew what the texts said was true.
So, assuming we can accept that the early church leaders can be credible in their testimony, what do they have to say about the authenticity of the Bible? As a whole, they do not add much to any evaluation of the OT. However, they do add quite a bit of evidence that the NT itself speaks truthfully in matters of history.
Polycarp was a disciple of John, the Apostle. Iranaeus was a disciple of Polycarp. These two men, who would have had access to a wonderful source of verification (John) quote 23 of the 27 NT books, and claim for them authenticity. Irenaeus even affirms the orthodox view of authorship of the four Gospels. This is important as discussed here because these four authors were eyewitnesses (Matthew & John), or had access to eyewitnesses (Mark & Luke). Polycarp and Iranaeus were also writing in the early 2nd century AD, and so were validating the NT historicity from very close to the times they described, being only one generation past the time in question.
In addition to Polycarp and Iranaeus, there are citations from NT books, or explicit declarations of their authenticity from men like Ignatius, Pseudo-Barnabas, Clement of Rome, Justin Martyr, Clement of Alexandria, Tertullian and Origen, all dating from no later than the late 2nd century AD, and covering nearly every NT book (3 John being the exception.) In other words, the early church, who were much closer to the events at hand, and had much more reason to know which texts were authentic, accepted virtually the entire NT canon. Barring a smoking gun proving the early church was cooking up a nice little conspiracy, there is no real reason to discount their witness to NT historicity.
More information can be found in this book, from which I drew the data above:
Geisler, Norman and Frank Turek. I Don't Have Enough Faith to Be an Atheist. Crossway Books, Wheaton Ill (2004).