Hi guys,
I currenly fail to make this old system working with a new DELL monitor to its native resolution of 2560x1440.
I was able to modify the Dell driver to be accepted by XP: Dell S2721DGF (HDMI1) with Intel(R) HD Graphics Pxxxx is shown.
But only can set the resolution to 2048x1152 Pixel 
Intel(R) HD Graphics Pxxx driver version 6.14.10.5449
Chipsetdriver Intel(R) 8 Series/C220 Chipset Family Desktop SATA AHCI Controller DEV_8C02 (added by Fernando) version 11.2.0.1006
Intel(R) Xeon(R) CPU E3-1245 v3 version 5.1.2600.0
Thank you so much 
@infuscomus
Thank you. Somehow my reply from yesterday is lost. Regarding to Intel the Intel(R) HD Graphics P4600 is capable via HDMI of 4096x2304@24Hz and DP 3840x2160@60Hz. DP in not on my board…
Alteranive if there is really no solution. What grafikcard is the latest to be running (with modded drivers) with XP? Like NVIDIA 750 1050 TI or similar from AMD?
Thank you.
----
Edited: I cannot post links
@guru1d
Officially for NVIDIA the fastest graphics card that works in XP is the GTX 960.
Unofficially the GTX 980Ti and TITAN (Maxwell) can also work in XP by adding their HWIDs to the nv4_disp.inf
For AMD I’m not 100% sure, I think the R9 270x is the last officially supported.
@infuscomus Just checked, the last graphics cards that support Windows XP are AMD’s 200 series and NVIDIA’s 900 series. Those are the last ones.
@infuscomus and @Aquavision Thank you.
Of course a solution for the onboard grafig would be appreciated.
@guru1d I’m afraid that’s not possible. AMD’s 200 series and before don’t support 2560x1440. Neither NVIDIA’s 900 series and before. I can’t help any further. Sorry.
What ?? I got the 2560x1440 resolution in WinXP on the old graphics card ATI Radeon 9550 SE