[Solved] Different bus/core ratio for replacement CPU

The bus-to-core ratio is called the multiplier. CPU makers produce similar CPUs with different clock speeds by adjusting the multiplier value. An otherwise-identical CPU with a different multiplier value and thus a different clock speed will absolutely be compatible in your unit. What you have to do is ensure that the faster CPU is in fact identical for everything except for multiplier/clock speed. You told us what the two CPUs are and they appear to be otherwise identical, so you should absolutely be able to put the T2600 in place of your T2300. The T2600 will simply run faster than your T2300 did, and the BIOS will automatically make sure that the new CPU runs at the correct speed.

You may also want to investigate and see if you might not be able to put one of the first Core 2 Duo CPUs in your computer as they are both higher-clocked and faster on a clock-for-clock basis compared to the Core Duo in your machine. The first Core 2 Duos are Socket M with a 667 MHz FSB like the Core Duos and use the same 945-series chipsets, so they are drop-in replacements for Core Duos in some machines. Your computer would need BIOS support for the Core 2 Duos, so you would need to check with Dell to see if they are supported.