I have a "SAPPHIRE 100259-1GL Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card" and a "EVGA E758-A1 3-Way SLI (x16/x16/x8) LGA 1366 Intel X58 ATX Intel Motherboard", is there a way for me to do a SLI or a crossfire?
You only can do SLI on SLI capable board... Well, since you already have HD4870 then the best you can do is stay with the card or sell it and get Nvidia cards, so you can SLI later on your motherboard...
+1^ That board supports SLI only,therefore you can use a single 4870 on it,but for 2 4870's or multiple ATI cards,you need a CrossFire compatible board.
Since there is no fee for enabling crossfire there is no reason to remove crossfire support from an X58 board. Many of them dont advertise it in their name since SLI is the rarer commodity but i havent seen one that didnt support it.
Fourth point under FEATURES section on the EVGA's Product Specification Sheet: