If it was running fine before you got your new monitor then it is probably your refresh rate.
Go into your monitor settings by right clicking desktop and going into display properties and find it from there.
The monitor is probably set to 60hz. Change that to 100 or 120 if you can. That will help a ton. Also it is basically a must do anyways. I have a 24" 144hz monitor and I typically run games at 1080p 120hz. If I went down to 60hz then it would definitely look very choppy. You can get used to 60hz after a while but if your previous monitor was set higher then 60hz and now your new one is defaulted at 60 then your eyes would definitely pick up on the difference.
If you still want a new video card, first find out what slots your motherboard has. I don't know how old your PC is, but it most likely has PCI-E. That is probably what your current card is as well. You may have power consumption issues trying to upgrade to a stand alone GPU. You could also be bottle necking your system depending on your other specs if you buy a newer video card.
Can you post the exact model of your Dell PC or the exact system specs?
I would have to see your system specs first, but here are a few $100-$200 cards that you could consider.
Your current card is PCI-E, so you know you can run PCI-E cards which all current GPU's are. Your current card has 1gb of ddr3 memory and a core clock of 650mhz and
80 steam processors with DVI output.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202113 $89 - 2GB 256-Bit GDDR5 memory - 880mhz core clock - 1536 Stream Processors - PCI-E 2.0
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150753 $109 - 2GB 128bit GDDR5 memory - 1050mhz core clock - 768 stream processors - PCI-E 3.0
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131545 $129 - 2GB 256bit GDDR5 memory - 900mhz core clock with boost - 1280 Stream Processors
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150733 $169 - 4GB 256bit GDDR5 memory - 1020mhz core clock with boost - 1024 Stream Processors
Those are just some quick picks, but I could get a better idea with the rest of your system specs. As you can see they are all MUCH better then your current card. If you only play that one game then you may not even need something as good as those. But with the first card being only $89 and still being much superior to your current card it gives you some insurance so you can get into some other games and be able to run them well. If your issue isn't with the new monitors refresh rate then you may NEED to get a new card if that current one can't handle the higher resolution of your new monitor. If you want to play some better games eventually then you may want to spend a little more. Think about it.
The biggest issue you may run into is your power supply. Usually power supplies on standard brand name PC's are not that powerful. It makes adding newer video cards a problem if the PSU doesn't have enough power to run it. Once you post your PC model we can find out what PSU it has and what your limitations are. For example, the cards in the links I provided require a PSU with a minimum of 500w to run. So if your PSU is only 450w or under that you may have to upgrade your PSU first.
PSU's don't cost too much, so if you do need one it won't put you back too much. You can get a good 600-700w PSU in the $50-$80 range. It is definitely a component that you do not want to skimp on quality though.