The Geforce 4 series is DX8.1 (excluding MX, which is really DX7, as its pretty much based on the Geforce 2). The 4800 is therefore DX8.1, so lacking the shader model 2 introduced with DX9.
By the way, the Geforce 5 (aka FX) series is DX9 (shader model 2), but REALLY bad execution thereof. Really need to go to Geforce 6 series.
On the ATI side, their Geforce 5 (FX) equivalent was the Radeon 9XXX which as quite good - avoid Radeon 92xx as these are DX8.1 also.