well I got a pentium 4 2GHz & 256mb ram with 160GB of hard disk memory & an Intel Graphics Card & I play esf on its highest settings & it runs smoothly but I guess its the Pentium 4 & the ghz thats helping me but i dont know...
Actually the Ghz doesn't mean squat.
A Pentium M 1.4Ghz is faster, than a 2.0Ghz Pentium 4.
The Pentium 4 was a good processor while it was up against the Athlon XP, But as soon as the Athlon 64, while even running at 1.8 - 2.0Ghz would out perform a 3.0 - 3.2Ghz Pentium 4.
Its not the clock speed, but instructions per clock that it can perform, a-la the IPC, And thats where the Pentium 4 lacked, It produced allot of heat, and consumed allot of power, and under-performed compared to the competition. (The Athlon XP around 2800+ and higher was on par, or slower than the Pentium 4, until the Athlon 64 was released).
Half Life is an old game, which uses a heavily modified Quake engine, It was released in a time where the 3DFX voodoo cards reigned supreme, and Pentium's and Pentium 2's were common, and having any more than 128Mb of ram was un-heard of.
Still, ESF is a mod, it has added extra features, and in turn, that will increase the system requirements, But realistically anyone these days should be able to run it.
For instance, When I goto the local dump, to... dump crap, More often than not I see a Socket 370 board, a Pentium 3 ranging from 400 - 1200Mhz, and 256Mb of ram, And more often than not if I bring it home it still runs, which in turn I either sell, for 100 bucks, or give it away.