Using the link that jkersenbr provided it is possible to overclock a Dell P4 system. However there are several variables.
First off, the motherboard has to offer 133 MHz as a possible speed. I don't believe the original i850's supported 133 FSB. However, it is possible that the board maker (most likely Intel) used a clock generator that does support 133 FSB. Your best bet would be to look on the motherboard and try to find the clock gen model number. Once you find this, then do a search on Google and try to find a datasheet. This should hopefully tell you what speeds are supported.
Second, the processor you're trying to overclock must obviously be a 100 MHz processor and must be albe to run at 133 FSB (preferably with default voltage). If it can run at 133 FSB but needs more than default voltage, then you can do the wire trick to increase the voltage but you want to be careful because the heatsinks in these systems are adequate but nothing spectacular. Your P4 1.9 GHz must not be a Northwood so it is highly unlikely that it will run at 133 FSB.