Intel i440BX does no more than 128 MBytes per DIMM side - 256-MByte double sided 16-chip DIMMs are the most recent it can use. Four of those gets you one GByte of RAM, and that's it.
Some server jobbies using this chipset support registered DIMMs, which lets you use 36-chip monster DIMMs for twice that much.
The difficult part will be to find either kind of DIMM for reasonable prices - 128-Mbit technology SDRAM is end-of-lifed with pretty much every DRAM manufacturer.
Now, harddisks. There's not actually a limit, since with IDE, the controller is in the drive. However, the DMA engine is on the mainboard - and I wouldn't trust ye olde PIIX4 to do 48-bit LBA mode, so I'd say 128 GiB is the technical limit. BIOS bugs might stop you earlier. Also, you're limited to UDMA-33.
Nothing keeps you from plugging a SATA or IDE controller onto the PCI bus though, relieving both those limitations.