Gateway, Dell and the other big boys lock the bios because they have learned from expirience that most of their costs for support came from having to deal with people tampering with the bios.
I believe ABit and some ASUS boards have good reputation for overclocking. ABIT IT7-Max2v2 & ASUS P4PE Deluxe are some examples of stable boards able to support overclocking to a certain extent.
Want overclocking? Go with AMD (1ghz of overclocking is possible). You want lower prices? Go with AMD. AMD performs better before intel's HT (Hyper Threading) processors came out. In that case, that would be ur 1.0GHz, but guess what, you can get a 1700+ for less than a PIII 1.0GHz.